In the Jeffersonian imagination, U.S. expansion is identified with the acquisition of acreage that could be settled by pioneer farmers (once the Native Americans or native Mexican inhabitants were dispossessed). But from the point of view of the policymakers who obtained them, these big chunks of territory were chiefly important as strategic seaports that happened to have thinly populated hinterlands attached. The United States did not abruptly switch under McKinley from overland territorial expansion seeking acreage for democracy-loving yeoman farmers to naval imperialism seeking bases in the service of militarists and greedy industrialists.

All of the great land grabs of American history were motivated in part by the desire to obtain strategic ports. The main objective of the diplomats Thomas Jefferson sent to negotiate with Napoleon in 1803 was obtaining the port of New Orleans, not the Louisiana Territory. The Adams-Oniz Treaty of 1819, which purchased Florida from Spain, and the U.S. annexation of “West Florida,” the Gulf Coast between present-day Florida and New Orleans, ensured access to the Gulf of Mexico. Many Americans believed that Texas had been included in the original Louisiana Territory purchase; from this perspective the annexation of Texas, which had been detached from Mexico by rebellious Anglo-American settlers and their native allies in 1836, was a mopping-up operation. When Mexico went to war with the United States over the annexation of Texas, the Polk administration, which had tried to purchase California, obtained its prize by conquest: the port of San Francisco. Earlier, the United States had risked war with Britain to partition the Oregon Territory, on terms that allowed the United States access to Vancouver Bay while leaving Vancouver Island in British hands. The purchase of Alaska from Russia by Secretary of State William Seward during Andrew Johnson’s administration in 1867 rounded off the continental domains of the United States.

Moreover, even though several of these sought-for ports and attached hinterlands were purchased or stolen from the weak states of Mexico and Spain, a major motive for their annexation by the United States was to deny them to more important powers who might obtain them, if they slipped free of control by Madrid or Mexico City or Paris. Thomas Jefferson purchased the Louisiana Territory from France, and James Monroe purchased Florida from Spain, to deny them to Britain. For ten years after the Texas Revolution of 1836, antislavery forces denied the admission of Texas to the United States as a slave state; the desire of British policymakers to keep Texas independent of the United States was a factor in persuading Congress to annex Texas in 1846. Keeping the Alaska Territory out of British hands was the motive for “Seward’s Folly.”

IN LIGHT of the Anglo-American rapprochement of the late nineteenth century and the deep Anglo-American alliance of the twentieth and twenty-first centuries, it is easy to forget how long the British Empire was viewed as the greatest strategic threat to the United States by American policymakers. Anglo-American geopolitical rivalry was central to both of the crises of the 1840s, the Oregon dispute and the Mexican War. Alta California, populated by around ten thousand Mexican nationals, had already achieved de facto independence from Mexico City, and it was widely assumed that the region would drift either into the U.S. or British spheres of influence, at a time when Britain was still the dominant naval and commercial power in North America. Americans who coveted California in general, and the ports of San Francisco and San Diego in particular, exaggerated but did not invent the possibility that California would become a British ally or protectorate, as Texas had threatened to become. The hope of some Southern secessionists that Britain would intervene to help the Confederate States of America obtain their independence from the United States, and the general preference of the British elite for the Southern rebels against the Union, shows that the danger that the United States would be hemmed in by British colonies or protectorates—Canada, the CSA, perhaps an independent Texas again and an independent California—was very real.

By the 1880s and 1890s, American fears of conflict with Britain were replaced by anxieties about the rise of Germany and Japan—anxieties which were not unreasonable, in light of the subsequent American wars with those nations. The naval buildup and quest for naval bases under McKinley and his successors, denounced by populists and liberals as an expression of un-American militarism or as a search for foreign markets by American big business, was in reality motivated largely by the belief of Alfred Thayer Mahan, Theodore Roosevelt and others that the British fleet could no longer protect American interests from an increasingly powerful Germany. Indeed, the conflict among the United States, Britain and Germany over Samoa; the Spanish-American War; and later U.S. intervention in the Mexican Revolution, which was, among other things, a proxy war between Imperial Germany and the United States, can only be understood as episodes in what was in effect a German-American cold war.

Defenders of the old-fashioned populist-liberal school of history might reply that American naval expansionists invoked rivalries with Germany and Japan as alibis for policies with other goals. But as the line often attributed to Henry Kissinger goes, even paranoids have real enemies. Between the 1880s and World War I, while building up its fleet, Germany sought its own Pacific island empire while hoping to expand its influence in Mexico, the Caribbean and Central and South America.

Merry notes McKinley’s concern about “ambitious nations—Germany and Japan in particular—interjecting themselves into the mess [in the Philippines] and spreading even more chaos.” This fear was well founded. Following the Battle of Manila Bay on May 1, 1898, the German squadron in Manila Bay outnumbered the American ships, and there was a tense confrontation between Admiral Dewey and German Vice Admiral von Diederichs.

Nothing can excuse the war crimes committed by U.S. troops in conquering the Philippines. There is also much to be criticized in the subsequent administration of the islands as a U.S. protectorate until after World War II, and in U.S. policy toward the Philippines since then. And the so-called “insular cases” that followed the Spanish-American War, in which the Supreme Court correctly ruled that Congress could limit the rights of inhabitants of U.S. territories, were abused by the administration of George W. Bush as an argument for the legality of torture and the denial of basic human rights in the U.S. base at Guantánamo, Cuba. But the McKinley administration was almost certainly right that a great power potentially hostile to the United States—most likely Germany, possibly Japan—would have made the post-Spanish Philippines a protectorate, if the United States had not done so.

Contrary to populist-liberal mythology, if Thomas Jefferson, John Quincy Adams and Ulysses Grant, among others, had been summoned from the grave in 1900 to learn that the United States had extended its control over Cuba, Puerto Rico and Hawaii, and was building a transoceanic Central American canal, instead of lamenting the replacement of the American republic by an American empire they probably would have been astonished that these acquisitions had been so long delayed. And they might have been surprised that Canada had not yet been absorbed into the American union.

PERHAPS THE greatest failing of the New Deal school of U.S. foreign-policy history is its failure to recognize the extent to which the central figure of the New Deal, Franklin Delano Roosevelt, was himself the heir of McKinley and TR. FDR is often portrayed as the second coming of Woodrow Wilson, in whose administration he served as assistant secretary of the navy. But his role model and hero was his cousin Theodore, whose footsteps he followed into the Department of the Navy and the White House.

FDR was a navalist of the school of Mahan and TR and Lodge. Under Wilson he presided over the U.S. occupations of numerous Caribbean islands, to avert possible German influence or sabotage. This record came back to haunt him, when he joked to a reporter during his campaign for the vice presidency in 1920: “The facts are that I wrote Haiti’s constitution myself, and, if I do say it, I think it’s a pretty good constitution.”

During World War II FDR came up with the name for the United Nations, but he was far more of a realist than Wilson. FDR hoped that the postwar world would be policed by a great-power concert of the major World War II allies—the United States, Britain and the Soviet Union—with the Chinese Nationalist regime enlisted as a pro-American fourth “policeman.” He seems to have envisioned not joint policing of every region of the world by the four founding members of the Security Council (to which France was later added), but rather distinct great-power spheres of influence, in which the United States, as the hegemon of North America and the dominant naval power in both the Atlantic and Pacific, would be first among equals. This idea of a sphere of influence in which the regional military hegemon exercises the “police power” against misbehaving neighbors, while the region remained open for commerce with the rest of the world, might be traced back to the (Theodore) Roosevelt Corollary to the Monroe Doctrine and the Open Door Doctrine in China announced by John Hay, the former secretary of Abraham Lincoln who served McKinley and TR as secretary of state.