President Donald Trump’s newest hero is William McKinley. In his second inaugural address, Trump called the oft-forgotten McKinley a “great president.” Much of that praise stems from McKinley’s love of tariffs. Yet what really marked McKinley’s presidency was his enormous expansion of American territory. McKinley presided over the acquisition of Cuba, the Philippines, Puerto Rico, and Hawaii.
Trump now appears to want to emulate McKinley’s 19th century real estate spree. He has insisted the United States must take back the Panama Canal (built during the administration of McKinley’s successor, Teddy Roosevelt), called Canada the “51st state,” and suggested the United States take control of Greenland as well. Indeed, in a confrontational call with the Danish Prime Minister—Denmark handles the foreign affairs of the vast Arctic island, a largely autonomous territory—Trump insisted he was very serious about Greenland. The Financial Times reported the Danish government, a NATO ally, was “utterly freaked out.”
Threatening friendly nations over their territory (or even unfriendly ones: international law has long disallowed threats to use force to acquire territory) is disturbing enough. But even if the current international legal order did not flatly prohibit forcible territorial acquisition, Trump may want to look more closely at McKinley’s rocky experience with new acquisitions before moving further down this path.
What McKinley Learned the Hard Way and How the World Has Changed Since
President from 1897 to 1901, McKinley was a Republican who presided over the defeat of Spain in the Spanish-American War. The war was in many respects America’s debut as a great power. In an age when empires served as markers of both power and prestige, a weakened Spain handed the victorious United States its former colonies in the Philippines, Puerto Rico, and Cuba. Hawaii become American territory through a contemporaneous annexation, one perhaps less bloody but sufficiently questionable that Congress, in Bill Clinton’s first term, apologized for America’s underhanded role in the overthrow of the Hawaiian monarchy.
Still, seizing all those distant islands turned out to be the easy part. In the decades that followed, the United States faced deadly and protracted insurgency abroad and legal headaches at home. And by the 1940s, the United States had let the biggest possessions—the Philippines and Cuba—go free.
One need not be a diplomat to recognize that any effort by the United States to seize Greenland or the Panama Canal will face strong condemnation abroad. Once a common feature of world politics, territorial acquisition by the threat or use of force has been unlawful since at least the end of the Second World War (and some would argue since the Kellogg-Briand Pact of 1928). Indeed, it is now understood as a bedrock rule of the international order.
The UN Charter specifically bars states from the “threat or use of force against the territorial integrity or political independence” of another state. This rule, embodied in a treaty largely drafted by the U.S. State Department, is binding on all states and reflects both customary international law and the hard-won experience of the Allies in defeating Axis aggression.
And even before the UN Charter era, territorial aggrandizement often yielded violent reaction. The Philippine-American War lasted for several years after the islands’ “liberation” from Spain—McKinley refused Filipino claims of independence–and served as the earliest known example of the widely condemned tactic of waterboarding as a form of torture by U.S. forces.
The Empire Strikes Back
What may be less obvious are the domestic challenges new territories raise. McKinley’s acquisitions were almost immediately disputed at home on a set of grounds that still resonate today. Some Americans at the time questioned whether U.S. imperial pretensions would destroy our democracy. But these new possessions also raised a host of novel legal questions, both mundane and sweeping, that resulted from the acquisition of territory that, unlike past examples such as the Louisiana Purchase, were not intended to become American states.
The core issue was how exactly the new territories fit into the American legal order. Did the Constitution “follow the flag,” in the language of the day? Or was the United States now like the other colonial powers of the day, ruling differently–and usually far more brutally and repressively–in its overseas possessions? Were the inhabitants of these islands now American citizens, or simply imperial subjects with a decidedly lesser set of rights and protections? And highly controversial at a time when tariffs were high, would goods—and people—flow freely between the new territories and the rest of the United States?
In the election of 1900 these questions were central. The Democratic Party made this the principal plank in its platform, declaring that the Constitution did follow the flag. Moreover, the Democrats argued, “imperialism abroad will lead quickly and inevitably to despotism at home.” Many Americans at the time nonetheless thought – as Trump apparently does today–that international competition and the pursuit of national wealth and greatness meant that the United States simply had to take over more territory.
Yet much like a dog that catches a car, the U.S. government seemed unprepared for the onslaught of difficult questions this sudden move to empire created. In January of 1900, the New York Times ran a headline that would be comical if the stakes weren’t so high: “Status of New Possessions: House Committee Named to Ascertain If They Are in Fact Parts of the United States.”
Legal challenges soon proliferated. In the so-called “Insular Cases,” the Supreme Court rendered a varied set of decisions about the new island possessions, united perhaps only by the opprobrium with which they are now remembered. Forced to find a way to reconcile American constitutionalism with rule over distant, overseas territories, the Court decided that only some of the Constitution applied to the newly-acquired populations. As a famous quip of the day went, the Constitution indeed may follow the flag, “but it doesn’t quite catch up.”
It is perhaps telling that perhaps the most influential of the Insular Cases involved a tariff question. In Downes v. Bidwell (1901) the Supreme Court had to decide if goods from the newly acquired island of Puerto Rico came from within the United States or were, instead, foreign goods. (One can readily imagine the same question arising with rare earths from Greenland.) Article I of the Constitution decrees that all duties, imposts, and excises “shall be uniform” throughout the United States. Did this provision now include Puerto Rico?
The public was surprisingly riveted by this question. A huge crowd gathered at the Supreme Court to hear the ruling, which the New York Times characterized as “one of the most tremendous events in the nation’s life.” But when the Court spoke, many had trouble following its reasoning. The opinion was checkered and confusing. Puerto Rico, the Justices declared, “is a territory appurtenant and belonging to the United States, but not a part of the United States.” In a bizarre and infamous phrase, the Court said the island was “foreign to the United States in a domestic sense.”
Similar difficulties arose with the Panama Canal. After engineering the breakaway of Panama from Colombia, the United States signed a treaty in 1903 with the new Central American republic that granted the United States, in perpetuity, the “use, occupation, and control of a zone of land…for said Canal.” Once the Canal was built, as a result, it was surrounded by a “Canal Zone” that was treated as American territory. But could a letter sent from the Canal Zone to Indiana now use a domestic stamp? Did the Bill of Rights apply to the government in the Canal Zone? And maybe more to Trump’s liking, did tariffs apply to goods that came into the Canal Zone from the rest of Panama? (The answers were yes to the tariffs, sometimes to the Bill of Rights, and yes to domestic stamps.)
These questions continued to arise for decades. In the 1940s, a federal court ruled that the Fifth Amendment’s due process clause applied to acts by the Canal Zone’s Governor. In the 1970s, however, a different court ruled that the Fifth Amendment’s rights did not apply fully to criminal defendants in the Zone, stating that the Constitution “does not require the extension of all protections of the bill of rights to territories governed by the United States.” These thorny constitutional dilemmas even continued into the 21st century. When the late Senator John McCain, born in the Canal Zone in 1936, ran for president in 2008, some queried whether he was, in fact, a “natural born citizen” as the Constitution requires.
The American experiment with acquiring distant possessions, in short, has had a very mixed record. The Insular Cases were front page news for years, and deeply divided our democracy. Those decisions largely remain on the books. But most lawyers, and even some of the conservatives on the Supreme Court, today view them with shame. Indeed, in 2022 in United States v. Vaello Madero, a case involving Social Security benefits for residents of Puerto Rico, Justice Gorsuch wrote
A century ago in the Insular Cases, this Court held that the federal government could rule Puerto Rico and other Territories largely without regard to the Constitution. It is past time to acknowledge the gravity of this error and admit what we know to be true: The Insular Cases have no foundation in the Constitution and rest instead on racial stereotypes. They deserve no place in our law.
While Hawaii and Puerto Rico remain U.S. territory—the former now a state, the latter still held in a quasi-colonial status–nearly all the other islands and zones were eventually released from American control. Cuba gained its independence in 1902, after a few years of American military occupation–and the condition that the constitution of the new Cuban republic contain a clause permitting the United States to intervene in order to “preserve” Cuban independence. (The United States, infamously, also retained its “coaling station” in Guantanamo Bay in perpetuity.) Though the Philippines signed the UN Charter in 1945, President Harry Truman only recognized Philippine independence on July 4, 1946.
During the Second World War the United States made the rollback of colonial rule a major part of its planning for the postwar world. Franklin Delano Roosevelt and Winston Churchill frequently grappled over the issue, which the United States saw as both values-laden—we now claimed to be strongly anti-colonial—but also, to be sure, driven by cold economics: in a free and open global economy, the strongest economy would dominate. The new United Nations contained, at American insistence, both a Trusteeship Council and provisions on “non-self-governing territories.”
The postwar United States nonetheless kept a big footprint abroad in the postwar era. But it mainly employed a vast array of leases and allies for its new strategy of forward deployment. The U.S. alliance system is intricate and sometimes complicated. But this network of allies is unprecedented and unmatched and helped the United States to win the Cold War. And it remains a primary distinguishing feature with the U.S.’ chief rival today, China.
Trump’s threats of simply taking new territory may, in the end, amount to nothing but bluster. But they not only risk a hornet’s nest of unexpected legal and political pitfalls of the sort his new hero William McKinley faced. Even more dangerously, they threaten the foundational rule prohibiting the threat or use of force against foreign territories, with all of the destabilizing consequences that may flow from undermining that bedrock norm. And perhaps most in tension with the stated interests Trump and his administration seek to pursue, these threats undermine U.S. national security by tearing apart the stability and depth of relationships with friends and allies that are critical to keeping the United States safe.