When Donald Trump first suggested that the United States should purchase Greenland, the reaction in Washington was disbelief mixed with ridicule. The United States, it had seemed, long ago settled its borders. Territorial expansion belonged to a different era.

　　Yet in the longer arc of American history, expansion has been quite normal. For much of the nation’s first century and a half, Americans debated not whether the United States should grow, but where and by what means. The idea that borders might shift was a routine feature of statecraft. So why does the idea now seem so strange?

　　Immediately after landing in North America, European colonists began spreading out. When the United States declared its independence, one of the Founding Fathers’ motivations was to move into new lands that Great Britain had closed to settlement. In the nation’s earliest days, its leaders did not treat its new borders as fixed. They were open to negotiation, purchase, conquest, and sometimes improvisation.

　　That assumption shaped the nation’s foreign policy from its earliest days. Before the Declaration of Independence, the Continental Congress authorized an invasion of Quebec, hoping to add another colony to the union. The effort failed, but it reflected the assumption that territorial expansion was both legitimate and desirable when it served the nation’s interests.

　　A few years later, the nation doubled its size through the Louisiana Purchase. The War of 1812 included another attempt to seize Canada. By the 1840s, the United States had extended its reach across the continent through a combination of negotiation and war. Political debates during this period tended not to question whether expansion was appropriate, but instead its extent. Should the nation take all of Mexico or only part? Was Cuba or Canada a better target? Should expansion continue into Central America?

　　For the first half of its independent history, expansion was simply how the United States operated.

　　At times, this ambition took forms that today seem strange. Private adventurers known as filibusters launched armed expeditions into Latin America to try to bring new territories under American control. After the Civil War, policymakers considered annexing the Dominican Republic, Haiti, Greenland, and various Pacific islands. Some of these proposals now seem implausible, but only because history turned out differently. The annexations of Alaska and Hawaii appear natural in hindsight, though they were once contested and uncertain.

　　By the late nineteenth century, however, American expansion had begun to change. The United States continued to acquire territory, including Puerto Rico, Guam, and the Philippines after the Spanish-American War. But this growth was becoming more selective. Policymakers increasingly sought limited strategic positions rather than large territorial additions. Opportunities for expansion were sometimes declined. Other territorial claims were abandoned.

　　After World War II, this shift became more pronounced. America emerged as the world’s dominant power, yet territorial annexation receded from its foreign policy toolkit. In Europe and Asia, the United States occupied defeated nations, reshaped their political systems, and established a lasting military presence. But it did not attempt to incorporate any new territory. Instead, the United States developed a different model of power. It came to rely on alliances, overseas bases, and economic institutions to extend its influence. It spread across the world commercially and culturally. These instruments provided many of the advantages that territorial expansion once offered without the burdens of sovereignty.

　　To understand this shift, it is useful to distinguish between two different ways of exercising power: control through ownership and control through influence. Annexation represents the first. It places territory—and the people who inhabit it—under the direct authority of the state. Influence, by contrast, allows a state to shape outcomes without assuming formal responsibility. It operates through relationships rather than incorporation.

　　The shift from annexation to influence was primarily a strategic adaptation.

　　For much of the nineteenth century, ownership was often the more straightforward option. If the United States wanted secure access to a port or natural resources, acquiring territory could solve the problem directly. But as the international system evolved, the balance shifted. Influence became both more feasible and more attractive.

　　Annexation, in turn, grew more costly. It required governing populations that might resist incorporation, integrating new territories into the constitutional order, and managing the political consequences of expansion at home. It also risked diplomatic conflict abroad, as norms of sovereignty hardened in the twentieth century. This shift reflected strategic concerns but was accompanied by a growing moral skepticism toward conquest after the devastation of two world wars. These costs were not always decisive, but they became increasingly difficult to justify when alternatives were available.

　　The language of self-determination, popularized in the World War I era, reshaped the debate around expansion. After the establishment of the United Nations in 1945, outright annexation carried a stigma that it had largely lacked in the nineteenth century.

　　And those alternatives multiplied after World War II. Military bases provided an opportunity to project significant force from a small footprint. Alliances reinforce security without territorial control. Economic institutions and trade relationships allowed the United States to access the world’s riches without redrawing maps. Even in cases of direct military occupation, as in Japan and Germany, the United States found it more advantageous to cultivate aligned, sovereign states than to pursue more territory.

　　America’s long history of interest in Greenland illustrates this transition. In the nineteenth century, the secretary of State considered purchasing the island, along with Iceland, as part of a broader vision of hemispheric expansion. In the early twentieth century, the United States traded away potential claims in Greenland while securing the more strategic Danish West Indies, now the US Virgin Islands. During World War II, American forces occupied Greenland and later sought to purchase it. Denmark declined, but granted the United States extensive military access. The strategic objective was achieved without annexation.

　　This is the pattern of America’s annexation history: A period of rapid territorial growth and vast ambitions, followed by a more selective approach to strategic annexations, and then an era of expanding control without expanding territory.

　　By the early twenty-first century, formal territorial expansion had largely disappeared from American policy debates. The United States had not abandoned the pursuit of power. It had altered the means by which it pursued it.

　　Recent proposals to acquire territory, such as renewed interest in Greenland, have been treated as aberrations. But they may be better understood as reminders that the underlying logic of expansion has not entirely disappeared.

　　The United States did not cease to expand simply because it rejected power. It stopped adding land because alternative methods of expansion proved more effective. The shift from annexation to influence was primarily a strategic adaptation, even as it was accompanied by a growing international aversion to conquest.

　　Whether that adaptation continues depends on the conditions that made it possible: a favorable international environment, the willingness of other nations to participate in American hegemony, and the effectiveness of economic and institutional tools. If those conditions change—if access to resources becomes more constrained, if alliances weaken, or if new forms of competition emerge—the assumptions that replaced territorial expansion may be tested.

　　For now, the United States continues to exercise power without redrawing its borders. That arrangement is not inevitable. The history of American expansion suggests that while the form of power can change, the pursuit of power remains constant.