his initiative. In mid-1913, El Salvador became the first nation to sign one of Bryan's treaties, and 29 other countries, including every great power in Europe other than Germany and Austria-Hungary, also agreed to sign the treaties. Despite Bryan's stated aversion to conflict, he oversaw U.S. interventions in Haiti, the Dominican Republic and Mexico. After World War I broke out in Europe, Bryan consistently advocated for American neutrality between the Entente and the Central Powers. With Bryan's support, Wilson initially sought to stay out of the conflict, urging Americans to be "impartial in thought as well as action". For much of 1914, Bryan attempted to bring a negotiated end to the war, but the leaders of both the Entente and the Central Powers were ultimately uninterested in American mediation. Bryan remained firmly committed to neutrality, but Wilson and others within the administration became increasingly sympathetic to the Entente. The March 1915 Thrasher incident, in which a German U-boat sank a British passenger ship with an American citizen on board, provided a major blow to the cause of American neutrality. The May 1915 sinking of RMS Lusitania by another German U-boat further galvanized anti-German sentiment, as 128 Americans died in the incident. Bryan argued that the British blockade of Germany was as offensive as the German U-boat Campaign. He also maintained that by traveling on British vessels, "an American citizen can, by putting his own business above his regard for this country, assume for his own advantage unnecessary risks and thus involve his country in international complications". After Wilson sent an official message of protest to Germany and refused to warn Americans publicly not to travel on British ships, Bryan delivered his letter of resignation to Wilson on June 8, 1915. Later career Political involvement During the 1916 presidential election, members of the Prohibition Party attempted to place Bryan into consideration for its presidential nomination, but he rejected the offer via telegram. Bryan supported Wilson's 1916 re-election campaign. Bryan did not attend as an official delegate, but the 1916 Democratic National Convention suspended its own rules to allow Bryan to address the convention; Bryan delivered a well-received speech that strongly defended Wilson's domestic record. Bryan served as a campaign surrogate for Wilson by delivering dozens of speeches, primarily to audiences west of the Mississippi River. Ultimately, Wilson narrowly prevailed over the Republican candidate, Charles Evans Hughes. When the United States entered