Each of the Progressive Era presidents—Republicans Theodore Roosevelt and William Howard Taft and Democrat Woodrow Wilson—was committed to protecting America's empire in the Pacific and to solidifying the nation's economic and strategic position in the Western Hemisphere. All were determined to guard the strategic approaches to the Panama Canal (acquired in 1903 and completed in 1914), expand U.S. trade with the Americas and China, and pursue balance-of-power policies in Europe and East Asia to ensure that no one power emerged to dominate those respective areas. Although they differed in techniques and rationales, the goals of the Progressive Era presidents were essentially the same, and they evoked little significant partisan opposition. Their approaches did: Democrats were particularly critical of Taft's dollar diplomacy and Republicans of Wilson's missionary diplomacy.
Woodrow Wilson led the United States into World War I to "make the world safe for democracy" and to safeguard American interests on the high seas. He and most of his countrymen regarded German submarine warfare as a threat to the nation's seafarers and to its economic health. They regarded Germany and its allies as totalitarian, expansionist powers who posed a threat to democratic societies everywhere. The majority of Democrats and Republicans enthusiastically supported the Wilson administration's decision to go to war. Indeed, Theodore Roosevelt had blasted the president for not coming to the Allies' aid earlier. The principal figure opposing the administration's preparedness policies and aggressive diplomacy was William Jennings Bryan, Wilson's first secretary of state. In the aftermath of the war, however, bipartisanship crumbled as Wilson sought to push his controversial peace program through Congress.
Wilson was an internationalist who envisioned a League of Nations that would act collectively to prevent aggression and war. His creation called for member nations to surrender a degree of their selfish national interests for the good of the community. When he and the Democrats in the Senate organized to push the Treaty of Versailles, which contained the charter of the League of Nations, through Congress, they found themselves opposed by two groups, both predominantly Republican. First were the so-called Lodge Republicans, who were determined to modify the covenant of the league. Personally, Lodge hated Wilson, but, in addition, the president had made no attempt to involve the Republican Party in the peacemaking process. The American delegation to the Paris Peace Conference of 1919 included neither a prominent Republican nor a member of the Senate. Finally, the Lodge Republicans were nationalists. They saw no reason why the United States should surrender its freedom of action and be committed by a majority of the league members to a course that was not necessarily in its interests. The other faction opposing the treaty was a group of isolationists, dubbed "irreconcilables" by the press, who were opposed to membership in an international organization under any conditions. Led by Senator William Borah of Idaho, the fourteen Republicans and one Democrat insisted that the United States ought to focus on domestic problems of poverty, ignorance, corporate wrongdoing, and political corruption. Many were midwestern Progressives who had more in common with Bryan and the Populists than they did with the eastern, business-dominated wing of the Republican Party. When Wilson refused to compromise with Lodge and his followers, the Senate rejected the treaty and with it membership in the League of Nations.