The History Of American Imperialism, From Bloody Conquest To Bird Poop

Feb 18, 2019


This is FRESH AIR. I'm Dave Davies in for Terry Gross. American presidents like to describe the United States as a force for freedom and independence in the world. Our guest, historian Daniel Immerwahr, says there are also plenty of times in our history when we've subjugated and ruled foreign lands - sometimes with bloody conquests. Today, roughly 4 million people live in the American territories of Puerto Rico, Guam, American Samoa and the Northern Marianas.

Immerwahr's new book is a colorful look at the history of and forces behind U.S. territorial expansion, including - and I'm not kidding - the need for massive quantities of bird poop in the 19th century. Daniel Immerwahr is an associate professor of history at Northwestern University and the author of a previous book "Thinking Small: The United States And The Lure Of Community Development." His new book is "How To Hide An Empire: A History Of The Greater United States."

Well, Daniel Immerwahr, welcome to FRESH AIR. Your book is about the growth of territories in the United States - those other than the states, which of course happened a lot as the U.S. expanded West. There were a lot of territories as the Native American population was pushed and pushed. Was there any single rule for their status or governance - these, you know, nonstate territories?

DANIEL IMMERWAHR: Well, I think you're right. It turns out that despite the fact that the name of the country is the United States of America, since its first day of being an independent country, it's been a collection of states and territories. And those territories have meant different things over different times. Sometimes they've filled up quickly with white settlers, such as California, and, within just a few moments, you know, in historical time, have become states. Other times, they've lingered for quite a long time. Puerto Rico has been a U.S. territory since 1899, and it's still a U.S. territory today.

DAVIES: An early territorial expansion over the seas - this is amazing - involved the pursuit of guano - I guess, you know...


DAVIES: ...Manure, which was needed for farmers who needed it for fertilizer. This was in the mid-19th century. How did this lead to an American push into the Pacific and Caribbean?

IMMERWAHR: Yeah. So you have to understand that in the 19th-century East Coast farms were suffering from something called soil exhaustion. And I'll confess that I had assumed that this was a sort of made-up 19th century thing, like hysteria in women or something like that. But it's very serious and very dire. And it turns out that one of the few things to restore nutrients to the soil is guano - namely the droppings of seabirds on generally remote, often Pacific islands that are in the middle of nowhere, where birds are just congregating and, you know, pooping year after year, century after century, and it's just piling hot in the sun.

This becomes an incredibly valuable commodity in the 19th century - white gold, they sometimes called it. And it was in pursuit of guano that the United States started annexing overseas territories and ultimately, starting in 1857, annexed almost 100 uninhabited guano islands in the Pacific and the Caribbean.

DAVIES: Right. And of course, somebody had to extract the guano. Companies were formed that did this for a profit. What were conditions like for workers extracting this stuff? Where did they come from?

IMMERWAHR: Well, I've asked around my 19th-century historian colleagues. And I think I can say with authority that guano mining - meaning being one of the people who extracts - who's actually marooned on the island and, you know, scraping the guano off - is possibly the single worst job that you can have in the whole 19th century. It's basically like coal mining, with all the kind of attendant lung damage, except to do it you have to be on a small, rainless island, and, you know, it might be three months before the next ship comes.

So the people who worked on the islands - so some of them were basically kidnapped from China. A few of them were tricked to get onto the islands. African-American men from Baltimore were sort of promised an idyllic, tropical work conditions. And then they arrived on a jagged, scorched island and were told that the next ship would be there in a few months. And if they wanted to get out of debt to pay for their passage, they had to have some guano to show for their time. Conditions on the guano islands were so bad that on one of the Caribbean islands - Navassa island near Haiti - the African-American workers mutinied and actually killed five of their white overseers.

DAVIES: This is quite a story - this island of Navassa near Haiti. African-Americans from Baltimore were recruited to come to this. What was the work like? Is it shoveling guano with, you know, hand shovels or what?

IMMERWAHR: Shoveling would be, I think, the happy version of it. I think a lot of it is blasting. I mean, you have to imagine that the guano and the Navassa phosphate is hardened into rock. So you blast it loose, and then that just kicks up all kind of dust in the air, which you inhale - sometimes the men would wear scarves over their faces to try to cut down on this. And this stuff smells terribly.

The guano ships - if they'd been carrying guano - often had to be retired from service or could only be used for guano because, you know, once you had been hauling guano, you can only be a guano ship. This smell is that bad. So their working conditions are really hard. And you have to do it out in the hot sun, right? I mean, one of the conditions of these guano islands that makes them guano islands is that there's not much rain on them. That's why the feces can pile so high. So it's really backbreaking work.

DAVIES: So there's this island - Navassa, near Haiti, where African-Americans were recruited from Baltimore to work digging the guano. There was a revolt. They - well, tell us what happened. They killed several of their overlords, right?

IMMERWAHR: Yeah. And so you have to understand it's not just that the work is really unpleasant. There's a whole regime of labor discipline. So you have to imagine these men - some of them might not have been literate - are told that if they just step on this ship, they'll step off the other end, and they'll be surrounded by beautiful women. And they'll be picking fruit, and occasionally they'll, you know, do a little guano work.

And then they arrive there. There's no women. The island is completely barren of fruit trees, except for one orange tree, which is on the overseer's estate. And they're in debt. And if they don't work hard enough, they go deeper into debt. If they transgress in any way, they get punished. And there's a particular form of punishment on this island - or by the men - are what's called triste (ph), which means they're tied up by their hands so that their feet are barely touching the ground, so they can barely support their weight. And they're just kept that way in the hot sun for hours. Not surprisingly, the men are, you know, really upset about this.

And eventually it leads, in the late 19th century, to a revolt. They just start throwing rocks. And then they recover some pistols and some dynamite, and they're actually able to fight their white overseers and kill a number of them, which is a major scandal in U.S. history. It hits all the newspapers. The newspapers run with these really sort of hysterical titles, like The Black Butchers because, you know, black men have killed five white men. And it hits - and it becomes national news.

DAVIES: Right. They're taken back to the states for a trial. And it both brings out interesting facts and some interesting legal principles. What happens?

IMMERWAHR: Yeah. So first of all, the conditions in Navassa start to become national news. And this island, which, you know, hadn't really been thought of a lot from the perspective of the U.S. mainland - suddenly everyone's, you know, reading articles about what it's like to work there. But the really interesting thing is this - so the men are going to be tried, and the Baltimore community - the black Baltimore community rallies around them, and they get a lawyer named E.J. Waring, who is the first black lawyer to pass the Maryland bar. And they get this great legal team behind them.

And the legal team not only points out the kind of awful conditions that the men work in. The legal team goes for this sort of Hail Mary legal strategy, which is to argue that the guano islands are not actually in the United States. So what the men did is not covered by U.S. law, and they cannot be tried in U.S. court. And actually these guano islands are foreign territory because the United States cannot claim overseas territory. It's unconstitutional.

Now, that's a interesting legal argument, and it goes very quickly all the way up to the Supreme Court. And the Supreme Court has to consider it. Ultimately, the Supreme Court decides that, no, these places are actual parts of the United States, and therefore the men can be convicted. But in doing so, it actually lays the basis for the legal foundation for the U.S. empire because it establishes the constitutionality of the fact that the United States can claim overseas territory and that is consonant with the U.S. Constitution.

DAVIES: Wow. And then the president, Benjamin Harrison, gets involved, and there's an interesting outcome.

IMMERWAHR: Yeah. So Harrison is struck by this - struck enough that he sends a warship to investigate and with a mission to, you know, see what's going on in Navassa island. And the ship goes. And the report comes back that conditions are absolutely terrible. They're worse than in prison, despite the fact that these men have committed no crime. And worse, there's not a lot that the workers can do to complain about it because, where are they going to go if they seek justice? They're just on an island, and the only other people there, besides the workers, are their white overseers. There's no court. There's no jurisdiction. There's nothing like this.

And Harrison takes this really seriously and decides that, OK, it is true that these places are part of the United States. That's an interesting novel, legal principle, and it's one he affirms. But that means that if these places are part of the United States, then the United States should be in them - that there should be jurisdiction over them. And they - and you can't just have a little private fiefdom. So he ends up commuting the sentences of the lead organizers of the Navassa revolt. Ironically - so they're no longer sentenced to death. Ironically they're therefore sentenced for the rest of their lives to hard labor.

DAVIES: And so the rulings establish the fact that the United States can seize foreign territory. The practice of seizing islands to mine guano ends when chemical fertilizers emerge. And these enterprises are largely abandoned. Do we still own any of the guano islands?

IMMERWAHR: Yes. The United States still does control and own - has sovereignty over some of those guano islands. Some of them, interestingly, it sort of forgets about. Once the guano is scraped clean, it allows Britain and France to gain control over them. And it doesn't really issue much of a protest. But some of them become really important. Those guano islands - these little spots in the middle of the Caribbean and particularly in the middle of the Pacific - become really useful in the 20th century because everything that is attractive about them to birds, you know, namely that they can be spots where you can land on - that also makes them attractive to airplanes.

And so in the 20th century, some of these guano islands get repurposed as key strategic military bases and airfields. It's actually on her way to one of the guano islands, Howland Island, that Amelia Earhart's plane goes down. She's planning to land on Howland Island because there aren't many spots in the Pacific that you can land and refuel.

DAVIES: Daniel Immerwahr's book is "How To Hide An Empire." We'll be back after a short break. This is FRESH AIR.


DAVIES: This is FRESH AIR. And we're speaking with historian Daniel Immerwahr. He has a new book about the history of the United States' overseas possessions and military outposts. It's called "How To Hide An Empire: A History Of The Greater United States." Well, U.S. imperialism really flowers with the Spanish-American War in 1898. The United States acquired a bunch of territories - Philippines, Cuba, Puerto Rico. How much of this military action was sold as saving the people in these colonies from Spanish oppression and how much because we just wanted to have overseas possessions?

IMMERWAHR: It's a little bit of both. In the late 19th century, there is a lot of talk and interest in the United States expanding overseas not just to small guano islands but to large colonies. And part of the reason for that is that the westward expansion of the United States, at least as measured by the United States Census, has stopped - that there is no more frontier, says the Census Bureau, as of 1890. So there's a number of people - Teddy Roosevelt being a really good example of them - who start talking about the need for the United States to create more frontier to expand into other territories.

And in this case, Roosevelt is very interested in territories - Spanish colonies, territories that are near the United States but that might be available. Spain is a relatively weak imperial power. And so it's partly with this kind of expansion in mind. And it's partly with a sense in the United States that there is a humanitarian crisis in Spain's colonies, one that, you know, is a crisis for the colonial subjects in Spain as they fight a bloody war against Spanish rule in Cuba, in the Philippines, to a lesser but serious degree in Puerto Rico. That might be an opportunity for the United States to insert itself. And it's a little unclear what's going to happen as a result of this.

But what does happen is a sort of imperial splurge whereby the United States enters the war that Spain is already fighting with its colonial subjects and provides a decisive burst of force at the end of the war, finally ending a war that, you know, from a Cuban perspective had been going on for years, from a Filipino perspective had also been going on for years. And as a result, the United States is in a position to claim a number of Spain's colonies. And it does - Guam, the Philippines, Puerto Rico. It briefly occupies Cuba. And then just sort of in a fit of enthusiasm during the same time, it also claims the Kingdom of Hawaii and American Samoa.

DAVIES: You know, the Philippines is a remarkable story. It's much larger than, I think, most Americans would've realized then or realize today. And as you say, I mean, there was a rebellion going on against the Spanish for many years. And the United States was in an alliance with this commander, Emilio Aguinaldo. So Admiral Dewey brings the U.S. fleet into the harbor of Manila in the Philippines. And you might think the two sides, the Philippine insurgents and the American military, come together to finish the conflict. What actually happens?

IMMERWAHR: Well, you might think that. In fact, that's what Emilio Aguinaldo. thinks. He's been assured, he says, by multiple officers in the United States that this is ultimately going to be a war for Philippine liberation. And so enamored is he by that prospect that he declares independence on behalf of the Philippines. And according to that declaration, the Philippine flag will be red, white and blue in honor of the protection and the humanitarian benevolence of the United States that is allowing the Philippines to seize its freedom from Spain.

So there is a really productive military alliance. The United States is able to defeat Spain's fleet while Aguinaldo, by land, using arms that are supplied by the United States, is able to send his forces to city after city and defeat the Spanish on the land. And, you know, the United States is not initially in a position to do that. It does certainly - doesn't have enough officers and men. So it's sort of watching from the shore as Aguinaldo racks up all these incredible victories. So it seems at first - it seems to many U.S. officers - it certainly seems to Aguinaldo - that this is an alliance.

It comes to an end in Manila. Together, the U.S. forces, now soldiers on land, and the Philippine forces surrounds Manila, where Spain has, you know - Spainsmen have holed up - and besieges Manila. And ultimately, it looks like it's going to be a fight together. But Spain cuts a deal with the United States, which is the following - the U.S. soldiers are permitted to enter Manila, fight a mock battle that will only last a very small amount of time with Spain, which is sort of an honor preserving thing.

And then the United States can take Manila, not the Filipinos. And the U.S. agrees to it. So it enters Manila, takes Manila, you know, runs its flag up the flagpole. And then, suddenly, "The Star-Spangled Banner" is playing.

DAVIES: And the Filipino insurgents were kept out of the city that they had besieged for so long.

IMMERWAHR: Yeah. And I can - I think you can imagine their shock as they think, God, we fought for this city. We fought, we thought, together with our allies. And suddenly, our allies have taken a city. And they haven't taken the city in the name of the Philippine people, which is what we thought the war was about. Suddenly, they've taken the city under the U.S. flag. And what's that going to mean?

And it turns out, according to the McKinley administration, that this is just the start. The military occupation of Manila is just the beginning of the U.S. military occupation and then annexation of the entire Philippines. And so the United States ends the war diplomatically by purchasing for $20 million the Philippines from Spain, which is, of course, a shock to Aguinaldo and all the men who'd been fighting with the United States under the assumption that this was a war for Philippine liberation.

DAVIES: So eventually, they subdue the islands. And is it true that, by one estimate, more people died in this conflict than in the Civil War?

IMMERWAHR: Yeah. So the estimate that you often hear - that the war killed 200,000 or perhaps 250,000 people. But there's a historian named Ken DeBevoise us who went through the census and, you know, did all the demographic calculations. And what he discovered - and I think this has been accepted by historians - is that the war actually killed far more people than that.

Once you add up not just the combat deaths but the disease deaths, which are really serious because the war unleashes diseases up and down the archipelago, you see that in just five years, the war killed something on the order of three-quarters of a million people, nearly all of them Filipinos. And that makes this war bloodier than the U.S. Civil War, which is also a war about secession.

DAVIES: So the United States ends up with these new possessions - the Philippines, Guam and Puerto Rico - Cuba for a period of time. And how did Americans think of this? Were they comfortable thinking of themselves as imperialists? Were they, like - the way the British were?

IMMERWAHR: Yeah, there's this really incredible moment right after these places are acquired where there seems to be a lot of enthusiasm in the United States for the notion that the United States is now an empire, that it's joining the imperial club with Britain and France. So I found these maps that cartographers produced right after 1898 and 1899. And these maps show the United States as you're used to seeing it - sort of the contiguous blob - but they also show boxes all over it. So Alaska is here. And the Philippines is there and Guam and Hawaii and American Samoa. And there's a real sense of excitement about this.

It's not just cartography. Writers start to try to come up with new names for the country because they sense that the United States of America actually doesn't quite work anymore because it's not a union of states. And they have a hard time imagining that Puerto Rico will be a state or that the Philippines will be a state.

So they think maybe the country deserves a different name. So they try out all kinds of different ones. Greater America appears in the title of a number of books. The Greater United States - that's a term that I thought was sort of artful and I ended up using. Oriental America, The Greater Republic, Imperial America. It's a moment of real sort of identity questioning for the country.

DAVIES: Daniel Immerwahr's book is "How To Hide An Empire: A History Of The Greater United States." After a break, he'll talk about how American presidents have dealt with overseas territories in the 20th and 21st centuries. Also, Kevin Whitehead reviews some live recordings from the 1960s featuring singer Jeanne Lee and pianist Ran Blake. I'm Dave Davies. This is FRESH AIR.


ISMAEL QUINTANA: (Singing in Spanish).

DAVIES: This is FRESH AIR. I'm Dave Davies in for Terry Gross. We're speaking with historian Daniel Immerwahr, whose new book, "How To Hide An Empire," tells the story of the United States' ownership of overseas territories, how they've affected the country's economic and security interests and, at times, tested its governing ideals. One of those times was after the Spanish-American War, when many Americans felt uncomfortable with the idea that millions of people in Spain's former colonies were now subjects, not citizens of the U.S.

Now, there was also the fact that with these territories, millions of nonwhites were now a part of American holdings. How did that figure into the way people considered this?

IMMERWAHR: It raises all kinds of interesting questions because the United States had understood itself to be a republic, meaning that the people who lived in the country would play some role in electing a government. And so now you have an interesting question. Does that rule still hold? Do Filipinos get to vote for the president. Do people in Hawaii get to vote? Do they have a congressman or something like that? There's a lot of resistance in the mainland United States to this kind of notion and a lot of sense that the people who are now part of the United States somehow shouldn't count as fully American, as fully part of the United States.

And the Supreme Court works this out legally with a set of cases that are called the Insular Cases, where it concludes that some of the overseas territories, despite the fact that they are part of the United States, technically - they're U.S. territory - they're not part of the United States in the constitutional sense. Namely, they're not covered by the Constitution. And if you are born in a U.S. territory that's not covered by the Constitution in this way, you don't have constitutional protections. You don't have the right to vote for president. You might not even have trial by jury. And in fact, this is still good law today. So if you live in the mainland United States and you travel to Puerto Rico, by virtue of having made that trip, you lose the constitutional right to trial by jury.

DAVIES: And yet, people in some of the territories were made citizens over time, those who weren't were U.S. nationals. Like, for example, Filipinos could emigrate freely to the United States, right?

IMMERWAHR: Yeah, there were times when there were some migration restrictions. You wouldn't think there should be any because these are all parts of the same country. But by virtue of that ruling whereby these places are not covered by the Constitution, there's the possibility of immigration restrictions, and at times, there are them. Yeah, so some people in the territories become citizens, but they don't become citizens in the same way that I became a citizen.

I became a citizen because I was born in Pennsylvania, and the 14th Amendment says, if you're born in the United States, you're a U.S. citizen. That has not been the case for people who live in the territories. Sometimes they're able to win legal victories that allow them to become citizens by birth, but those - even that is not constitutionally guaranteed. And even today, if you're born in American Samoa, you are a U.S. national. You are not a U.S. citizen by birth. Your passport looks different.

DAVIES: So essentially, the Supreme Court said, Congress can decide what the rules are in the territories, right?

IMMERWAHR: Yeah, and that's the history, is that Congress ultimately has discretion about what happens in the territories.

DAVIES: Right, and some were enthused about this imperialist - these imperialist acquisitions and having the United States join the imperialist club. Was there a backlash? Were there - were there those who said, this is a terrible idea, this is an abrogation of who we are?

IMMERWAHR: Yeah, I think it's really important to remember that becoming a forthright empire in the way that the United States did in 1898 and 1899 was not uncontroversial. There were a lot of people in the U.S. mainland who objected strenuously to it. A really good example of that is Mark Twain. Mark Twain was a dogged anti-imperialist, and he wrote with withering sarcasm about the Philippine war and about the massacres that took place as part of it.

And he wasn't alone. There were a lot of people who were made really uncomfortable by the territorial expansion of the United States, some of whom thought it was a violation of the Republican values of the country, others of whom were racist and just objected to the idea that there would be more non-white people in some way included in the country.

And the anti-imperialist movement is a weird combination of, on the one hand, the black thinker W. E. B. Du Bois, and on the other hand, extreme hardcore racists, like this guy Senator Pitchfork Ben Tillman, who just object to the notion that any - any more non-white people would be part of the country.

DAVIES: So we get up to World War I, which was a conflict that redrew an awful lot of maps. And there were a lot of colonized people in many parts of the world who expected, as they, you know, supported the countries that colonized them in the war, expected independence to result at the end. They were sorely disappointed. The European powers kept most of their colonies.

Our president was Woodrow Wilson, who was an advocate of, you know, international cooperation in the League of Nations. What was his attitude towards foreign possessions on the part of the United States? Did the United States shed colonies or acquire them then?

IMMERWAHR: Wilson is a really complicated figure in that way because you can find a lot of moments where Wilson talks about empire in a really critical way. And I think a lot of that had to do with his own background, where he had been in the South during the Civil War, and particularly he'd been in the South during Reconstruction, when the South had basically become, as Woodrow Wilson understood it, a conquered possession of the North. And a lot of the bitterness that Wilson felt during Reconstruction allowed him to be a sort of anti-imperialist in a very interesting way.

Yet, at the same time, Woodrow Wilson - and this is another legacy of growing up in the South and having a father who had written a pamphlet, indeed, defending the biblical right of masters to own slaves - Woodrow Wilson was also a racist who, in his historical writings, was really enamored of the Ku Klux Klan, and who watched and acquiesced as, during his presidency, the federal government was segregated.

So which side of Wilson would come out in World War I was a really interesting question. Wilson had said that he hoped that the Philippines would no longer be a U.S. colony. Now, what exactly that meant is a little hard to say. But at the end of World War I, Wilson had so much power to rewrite the rules of the international order. And so many anti-colonial activists - Gandhi, Saad Zaghloul in Egypt, Ho Chi Minh, who was living in Paris at the time - gravitated toward Wilson, hoping that he would use that power to break empire.

And that's also true of people within the U.S. empire. A figure named Pedro Albizu Campos tries to go to Paris at the end of the war to get Wilson's ear. And I think, tragically, Wilson refuses to hear any of these people and ends up basically affirming a world order that is still safe for empire, where empires are left intact. And this was bitterly disappointing to Pedro Albizu Campos, to Gandhi, to Saad Zaghloul, to Ho Chi Minh. Many of them sort of learned a sort of resentment of the United States in that moment and a resentment that they would carry with them for decades.

DAVIES: Right. And actually, under Wilson, the U.S. purchased the Danish West Indies, which became the U.S. Virgin Islands, so...

IMMERWAHR: Yeah, not only did the United States fail to let Puerto Rico become independent, as Albizu had hoped, it actually acquired a new colony - the U.S. Virgin Islands - which it has today.

DAVIES: So Puerto Rico remains a U.S. territory after World War I. Its inhabitants were made American citizens in 1917, right?

IMMERWAHR: Yes, that's right. And that's part of a hope to draw them into participating in the war. They're sort of offered citizenship as a way to assure the United States that Puerto Rico won't stage a revolt during the war, won't create problems for the United States during the war.

DAVIES: Right, and Pedro Albizu Campos, who organized the nationalist movement, actually enlisted in the U.S. Army to go fight in Europe, right?

IMMERWAHR: Yeah, he was down for it. He was ready to fight. And he was ready to fight on the understanding that Puerto Ricans fighting for their country - which he understood to be the United States - would win the respect of their fellow co-nationalists on the mainland, and would encourage Wilson to make good on what Albizu considered the promise of Wilsonianism and would let Puerto Rico become independent. Now, Albizu was bitterly disappointed by this, and it's after World War I and the disappointments that he becomes a nationalist, rather than sort of enlisted lieutenant in the U.S. Army.

DAVIES: Daniel Immerwahr's book is "How To Hide An Empire." We'll be back after a short break. This is FRESH AIR.


DAVIES: This is FRESH AIR. If you're just joining us, we're talking with Daniel Immerwahr, author of the new book "How To Hide An Empire: A History Of The Greater United States." When we left off, we were talking about Puerto Rico's independence movement after World War I.

There's a part of this story that's fascinating, which I don't know that I ever heard about - an American doctor, Cornelius Rhoads, who was...


DAVIES: ...On the island in the 1930s, working in public health to alleviate disease. He authored a letter that proved pretty incendiary. What happened?

IMMERWAHR: Yeah. So Cornelius Rhoads had been working for the Rockefeller Institute. And he'd come to Puerto Rico to study anemia. And he took the fact that he was in Puerto Rico as sort of license to do whatever he wanted. So he immediately started running all kinds of experiments that it's almost impossible to imagine him doing on the mainland - certainly not on white patients. So he refused to treat some of his patients just to see what would happen with them. In other patients, he actually tried to induce disease in them. He described them to his colleagues as experimental animals.

And then came the letter - he sat down and wrote this letter, which is notorious in Puerto Rican history, where he said, first, you know, the island is a beautiful place, but the problem is it's full of Puerto Ricans. And they're dirty. They're thieving. They're one of the worst races that inhabits the planet. And the best thing to do for Puerto Rico, he says, would be to totally exterminate the population. And then he says, to his colleague in Boston to whom he's writing, I've started that already. I've killed eight of my patients, and I've tried to transplant cancer into 13 more although none of them have died yet. And this is just a chatty letter that he's writing to a colleague in Boston. And it gets discovered. And when it gets discovered, it becomes an explosive issue in Puerto Rican politics and helps to fuel the nationalist movement of Pedro Albizu Campos.

DAVIES: And there were some violent outbursts associated with that. What became of Dr. Rhoads?

IMMERWAHR: Oh, it's incredible. So one of the things that's really extraordinary about this story is that, after this all comes out, Rhoads just leaves. He just leaves Puerto Rico. He goes back to New York. There's - he never faces a hearing. He never faces trial. There is an investigation in Puerto Rico, but it's done by the colonial government, which is appointed rather than elected. And in the course of it, the governor discovers another letter, which he deems worse than the first and destroys.

So the government destroys incriminating evidence. We don't know exactly if he killed eight people or not. He says he was joking. He says it wasn't real. And it's hard to tell. But one of the reasons it's hard to tell is that the government destroyed incriminating evidence.

Rhoads meanwhile goes back to the mainland, isn't even fired. Not only is he not fired, you know, within years, he becomes the vice president of the New York Academy of Medicine. And then he's inducted into the Army during World War II. He becomes a colonel. And from that position, he's the chief medical officer in the Chemical Warfare Service.

So the United States is trying out all kinds of poison gases and other chemical weapons. And a lot of the way it tries those out is by doing human subjects testing on uniformed men - it turns out 60,000 in all. These men are - have mustard agents applied to their skin. They're put in gas chambers with gas masks just to see what happens. And the United States also has an island near Panama that it claims and that it uses to run all kinds of chemical weapons tests. A lot of the men who are tested on on that island are Puerto Ricans.

Cornelius Rhoads is right at the center of this. He's the chief medical officer. He's the one who ultimately has to sign off on the ethics and the medical advisability of these tests. And I've gone through the records of the Chemical Warfare Service and haven't found a single test that he objected to. Just the opposite - he goes through, and he comments on the tests. Does white skin blister differently than black skin? Let's find out. Here's what Cornelius Rhoads has to say. So he has this really incredible history, after having already left the island, of still experimenting on more Puerto Ricans.

DAVIES: So he finishes his career as a respected physician but is remembered on the island of Puerto Rico.

IMMERWAHR: He's remembered on the island of Puerto Rico as a sort of villain - the thing that spurred the nationalist movement. The odd thing is that's not how he's remembered on the mainland because, as a result of all of these chemical weapons testing, he and a number of other doctors are able to observe that some of the chemical agents are actually good at fighting cancer.

So Cornelius Rhoads then, with a number of other doctors, becomes the head of the Sloan Kettering Institute. And he sets up in a hospital, and he becomes one of the forefathers of chemotherapy. He's on the cover of Time magazine. He's celebrated for decades as one of the pioneering doctors in the United States.

And that celebration only works because the people who are celebrating him within the medical community in the United States - there's, like, an award named after him that goes to promising cancer researchers - but no one in this medical community has any sense of his past history in Puerto Rico. The informational segregation is so complete that ultimately he gets away with it.

DAVIES: At the end of World War II, it's - you know, the United States had all of these foreign territories - you know, the Philippines, Guam, American Samoa. And it was also occupying Japan and part of Germany - and probably other places that I don't know of. It's striking that you say that at one point there were 135 million people overseas under American jurisdiction - more than actually lived on the mainland.

IMMERWAHR: Yeah. If you look at the end of 1945, and you add up everyone who's living in the U.S. colonies and in the U.S.-occupied zones - which includes Japan, South Korea, part of Germany, part of Austria - it turns out that there are more people who are living outside of the States but under the U.S. flag than who were living inside the States.

DAVIES: And the United States then decided to, in effect, decolonize - to shed itself of territory rather than tighten its grip, as happened in many cases after World War I. Why did it move in this direction?

IMMERWAHR: Yeah. You can imagine a possible history in which the United States used its territorial leverage and its military leverage at the end of World War II to just go on a sort of imperial splurge and to take every colony it could. Certainly there would be very little to militarily stop it doing so. But that's not what happened. The United States - that's right - decolonized. It didn't entirely do so - I mean, it still has territories today. But it did significantly distance itself from territorial empire.

So the Philippines became independent in 1946. Hawaii and Alaska were promoted to statehood, against the objection of racists. And even in Puerto Rico, which still remains a territory, there was a constitutional change such that it was a commonwealth now, which ostensibly meant that it was no longer - at least by the United Nations' measurement - a non-self-governing territory.

DAVIES: Why was that the direction, you know, our leaders took at the time?

IMMERWAHR: Well, I think there's two reasons. And one of them has very little to do with the leaders themselves, which is that by World War II there was a worldwide anti-colonial revolt. The war had destabilized empires so much. And for decades, anti-imperialists had been organizing and arming themselves, that by the end of World War II, it's actually fairly hard to stuff the genie back into the bottle. And there were anti-colonial armies, including in the Philippines, that were on the march that made retention of empire just a much more difficult proposition than it had been at the end of World War I.

But there's something else that happened too was that during the war, the United States develops all kinds of new technologies, technologies that gave it a different kind of relationship to territory and technologies that made it possible for the United States to expand in its power without actually going on a sort of land grab.

DAVIES: You know, you note in the book that the British Empire was celebrated by its citizens at home. There was actually an Empire Day and a big colonial structure that was seen as not just expanding British influence around the world but improving and civilizing its subjects in many continents. We've never quite had a sense of ourselves as an imperial country. How do you think Americans view their overseas possessions and expeditions?

IMMERWAHR: Well, I think they often don't view them. Most people who live on the mainland think of the United States mainly as a republic and are peripherally aware perhaps that Puerto Rico is part of the United States. But still, even after Hurricane Maria, which devastated Puerto Rico and pushed the island into the news, only a bare majority of people on the mainland when polled were able to say that Puerto Ricans were U.S. citizens.

So I think that the culture of just not recognizing the imperial dimensions of the United States is really strong and has been going on for quite a long time. Woodrow Wilson had a really evocative way of putting it. When he was speaking of the territories, he said, you know, the thing about them is that they lie - this is what he said - outside the charmed circle of our national life. And that's an unfortunate thing, but I think that's probably still true today.

DAVIES: Well, Daniel Immerwahr, thanks so much for speaking with us.

IMMERWAHR: It's been a pleasure. Thanks so much.

DAVIES: Daniel Immerwahr is an associate professor of history at Northwestern University. His new book is "How To Hide An Empire: A History Of The Greater United States." Coming up, Kevin Whitehead reviews some live recordings from the 1960s featuring singer Jeanne Lee and pianist Ran Blake. This is FRESH AIR.