Woodrow Wilson, elected president in 1912, introduced what would be known as the New Diplomacy. His conception of this policy evolved gradually as the Great War in Europe progressed. Convinced that the European balance of power, from which the United States was excluded by the Monroe Doctrine, was the main cause of the war, Wilson envisioned international relations based on "a world safe for democracy." For him this meant equality of rights between states both large and small, replacement of an equilibrium based on violence by maintenance of peace through the creation of a league of nations, and abolition of secret treaties in favor of "open covenants openly arrived at" (the first of the Fourteen Points of 8 January 1918). In his eyes, the mission of the American people, which he considered morally superior to other peoples by its composition and its democratic tradition, was the establishment of a lasting peace.
When Germany resumed its unrestricted submarine war on 1 February 1917, thereby violating the rights of neutral parties, Wilson, on 2 April, proposed to Congress that the United States enter the war. From this moment it became clear that the greater their role in the war, the more Americans would be in a position to impose the New Diplomacy on their associates, with whom they were careful not to link themselves by alliance.
Subsequently, Wilson exerted considerable influence on the negotiation and conclusion of a number of treaties, most notably the Treaty of Versailles (28 June 1919). Regarding the negotiation of that treaty, Wilson imposed several important breaks with tradition on the Europeans. He announced that he would lead the American delegation himself, a step that caused a delay in the opening of discussions until 18 January 1919. He demanded that the Allies, following Germany, adopt the Fourteen Points before the signing of the armistice of 11 November 1918. He stipulated that the Covenant of the League of Nations must be drawn up before territorial, military, and economic issues were dealt with. Finally, Wilson wanted the Allies and associate powers to reach an agreement among themselves before imposing the treaty on Germany (a step that gave the treaty the appearance of a diktat).
When it was time to conclude the treaty, Wilson, supported by British Prime Minister David Lloyd George, obliged France to renounce permanent military occupation of the Rhineland in exchange for two treaties (one Franco-American and the other Anglo-French) guaranteeing France's national boundaries. Wilson also delayed indefinitely the satisfaction of Italy's claims to Austrian territory and colonies. On the other hand, he had to yield to Japanese demands to acquire Germany's rights in China. The Japanese had threatened, first, to insert an article on racial equality in the Covenant of the League of Nations and, then, not to join the organization. Finally, Wilson and French Premier Georges Clemenceau forced Lloyd George, who was sympathetic to German objections and would have wanted to soften the terms of the treaty draft, to agree to keep it much as it had been presented on 7 May 1919 to the German delegation.
But Wilson failed to obtain ratification in the U.S. Senate. He made the error of not inviting any senators to participate in the negotiations. Since November 1918 the Senate membership had included forty-nine Republicans and forty-seven Democrats. The chairman of the Senate Foreign Relations Committee, Henry Cabot Lodge, was a personal enemy of Wilson's. The Senate was bitterly divided on the issue of support for the Treaty of Versailles and U.S. membership in the League of Nations. In a vote, which had to approve the treaty by a two-thirds majority, Wilson could count on a maximum of only fifty-eight votes, while a two-thirds majority required sixty-four. It was clear that the Senate would accept the treaty only with major amendments.
Wilson refused to seek a compromise. He overestimated the support of world public opinion for the league as well as his own influence in the Senate. From 3 September to 29 September, Wilson traveled across the United States in order to arouse public support. The exertion was too much for him, and he became seriously ill. Sheltered from contact with the world by his wife and his physician, who withheld bad news, he obstinately refused any compromise, even though he was advised to do so by the Allies themselves. The Foreign Relations Committee agreed to condense all its objections into fourteen reservations, known as the Lodge Reservations. These were mostly aimed at denying the league the right to impose any obligations or restrictions on the United States (such as military sanctions), at rejecting any intervention of the league in internal affairs, and at exempting the Western Hemisphere—the area covered by the Monroe Doctrine—from sanctions of any kind. The text finally submitted to the Senate on 19 December was not the treaty but the treaty plus the Lodge Reservations. On 18 March 1920, in a surprise move, a fifteenth reservation, calling for the independence of Ireland, was added. On 19 March a final vote was held on the treaty plus the Lodge Reservations plus the fifteenth reservation. With only forty-five in favor, the two-thirds majority was not reached and the treaty was definitively rejected. The new president elected in 1920, Warren G. Harding, was a nationalist hostile to the League of Nations.