Diplomatic history traditionally holds 1898 as the year that the United States emerged as a world power.

During the 1880s (a decade earlier), the United States maintained one of the world's strongest economies and largest populations, and by these metrics it had already achieved great power status. But these metrics--especially back then--do not alone define a "world power." The ability to influence world events was the defining feature of a world power, and by this measure the United States lagged far behind its European contemporaries. The Berlin Conference of 1884 had initiated the so-called "Scramble for Africa," and over the course of the next few decades the European powers colonized practically the entire continent. At the same time, European powers held territories elsewhere--Britain had ruled over India for years, and France established French Indochina in that same decade. And while imperialism was not the only measure of a nation's ability to influence world events, it was both a clear manifestation of this power and the most important measure of the period. To be sure, the United States participated in the practice of imperialism as well. As Fareed Zakaria explains, by 1890 "the United States acquired forsaken Alaska and the tiny Midway Islands and gained basing rights in Samoa. During the same period, Britain and France each acquired over three million square miles of new colonies." At the end of this decade, the United States had the potential to become a world power, but it had not yet converted this potential into world-power status.

By the end of the 1890s, the United States had made strides in several important ways towards becoming a world power: it had surpassed all other economies in output to become the definitive economic power, developed a world-class navy, expanded its overseas territories into a clear empire, and, through an influx of immigrants, swelled in population so as to dwarf all of the European powers except Russia. The growth in industry and population may have been the natural course for the ever-growing United States (and it surpassed the British economy in total output in 1895), but its naval expansion and war with Spain proved to be divergences from its history. Over the course of the 1890s, the United States, influenced by Alfred Mahan's The Influence of Sea Power Upon History, 1660–1783, used its ever-increasing economic power to join the international naval arms race in force with many within the Navy harboring the ultimate goal of converting the United States into a world power.

Then, in 1898, the United States went to war with Spain. Ostensibly, the United States went to war to help Cuban resistance fighters earn their independence from Spain (there's more to this story, such as the sinking of the American battleship Maine and the yellow journalism that supposedly helped cause the war by publishing exaggerated stories about the sinking of the Maine and other Spanish evils), although the desire to increase American power played an obvious role as well. The war proved short and one sided, with the United States handily defeating Spain in a matter of months. This led the two powers to quickly negotiate the 1898 Treaty of Paris, in which the Spanish ceded territories, including Cuba, Guam, and the Philippines, to the Americans. The United States essentially inherited an empire from Spain. Of course, the United States could have simply freed all of these people from Spanish control as it had indicated it would at the start of the war. Instead, it forced Cuba to adopt a constitution that deferred its foreign policy to the United States (the United States could not outright annex Cuba after having ostensibly fought for its independence) and it went to war with the Philippines in order to turn the nation into an American colony.

By the year 1900, the United States had transformed from a potential world power into one of the world's preeminent powers. The nation had shocked Europe, most of all Spain, by easily defeating one of Europe's global powers (even if that power had been on the decline for decades). Moreover, Americans now perceived themselves as a world power. And by consolidating their new territories rather than simply allowing them to go free, the Americans revealed a previously unseen willingness to project power across the globe. The United States was no longer an economic power that might become a world power one day; it was the economic power, and it displayed a new desire to use this power to promote its interests across the globe.