As long as this policy was regarded as natural and obvious, it provided no basis for factional disputes and required, therefore, neither ideological nor programmatic definition nor a specific label. Isolationism emerged as a distinctive and definable political position only when the foreign policy consensus derived from the teachings of Washington and Jefferson began to break down, a development that found its basis in the conditions of the late nineteenth century but full expression only in the period of World War I.
By the end of the nineteenth century, virtually all of the circumstances that had made the traditional policy of the United States possible had either been greatly modified or disappeared altogether. With rapid industrialization and the opening of vast new lands to agriculture, the United States had become a serious factor in the world economy and was converting itself from an importer into an exporter of capital. The need for the protection of trade and investments, as well as the chauvinistic search for the sinews and symbols of power that infected all Western nations in these years, led the United States to follow the teachings of Alfred Thayer Mahan, who in his lectures at the newly established Naval War College—subsequently published as The Influence of Sea Power on History, 1660–1783 (1890)—argued that great countries were built by great navies. Even as the United States thus embarked on the road to military power, advances in technology and communications continued to shrink the oceans and thereby to move the country from the periphery of power to a place closer to the center. And the nineteenth-century balance of power, which, for all the abuse that had been heaped on it by American statesmen, had served the nation well, was upset by the simultaneous rise to international prominence of two ambitious newcomers, Germany and Japan.
The United States responded to these changes with a more active foreign policy and greater international involvement. In 1884 it joined the International Red Cross and participated in the Berlin Conference that was intended to solve the problems in the Congo. Three years later, it hosted the first international conference of its own, the Washington Conference on Samoa, and in 1889 the first Pan-American Conference. These expanded international contacts soon led to further involvement. The Venezuela Crisis of 1895 was followed by the War with Spain, the acquisition of Hawaii, Puerto Rico, and the Philippines, and the enunciation of the Open Door policy designed to assure equal international access to the markets of China. The United States sent delegates to the First International Peace Conference at The Hague in 1899, and the following year contributed 5,000 troops to an international expeditionary force that put down the Boxer Rebellion in China.
The pace of America's involvement with the world quickened during the presidency of Theodore Roosevelt, who hugely enjoyed asserting America's growing power. In 1902, after Great Britain, Germany, and Italy had blockaded Venezuela and brought its dictator, Cipriano Castro, to his knees, he facilitated an arbitration of the dispute that protected America's long-standing interests in Latin America. In 1903 he encouraged rebellion in Colombia, promptly recognized the new country of Panama that emerged, and acquired territory from it on which to build a trans-isthmian canal. In 1904 his corollary to the Monroe Doctrine arrogated to the United States the exercise of an international police power in the Caribbean, and for the next twenty years U.S. marines landed periodically in Cuba, the Dominican Republic, Nicaragua, Haiti, and, on occasion, even Mexico. In 1905 he mediated the peace treaty between Russia and Japan that was concluded at a conference in Portsmouth, New Hampshire. For his efforts he became the first of three Americans who were to win the Nobel Peace Prize before 1920.
All of this activism in international affairs was deemed to be compatible with the foreign policy of the Founders, and the traditional American consensus therefore remained largely intact. Even the anti-imperialists at the turn of the century, while opposing the acquisition of colonies on the grounds that this would fundamentally change the character of the American Republic, made surprisingly little of the fact that it would inevitably lead to involvement in the great power rivalries against which President Washington had warned, and that the Open Door policy would have the same effect if attempts were made to enforce it. When the Senate ratified the Algeciras Agreement of 1906, an international compact dealing with the future of Morocco, and the Hague Convention of 1908 that established the rights of neutrals and of noncombatants—both clearly "entangling" in nature—it simply added the proviso that agreeing to them was "without purpose to depart from the traditional American foreign policy."
Less than three months before the outbreak of World War I, Woodrow Wilson, who still insisted that "we need not and we should not form alliances with any nation in the world," reasserted the traditional policy: "Those who are right, those who study their consciences in determining their policies, those who hold their honor higher than their advantages, do not need alliances." Consequently, the onset of hostilities in Europe produced the traditional American response: a declaration of neutrality and a reassertion of the policy of friendship with all and entanglements with none, which, as an editorial in the magazine World's Work put it, "was made for us by wise men a hundred years ago."