1. Lusitania Sinking: In May 1915, a German U-boat sank the British passenger ship Lusitania, resulting in the deaths of 1,198 people, including 128 Americans. This incident sparked widespread outrage in the United States and increased pressure on Wilson to take action against Germany.
2. Zimmermann Telegram: In January 1917, the British intercepted and decoded a secret telegram sent by German Foreign Secretary Arthur Zimmermann to the German ambassador in Mexico. The telegram proposed a military alliance between Germany and Mexico against the United States, promising to support Mexico in recovering territories lost in the Mexican-American War. This revelation further intensified public sentiment against Germany and strengthened the case for war.
3. Unrestricted Submarine Warfare: In February 1917, Germany announced it would resume unrestricted submarine warfare in the Atlantic, targeting both Allied and neutral ships. This decision posed a direct threat to American merchant vessels and increased the risk of American casualties.
4. Public Support: Despite Wilson's initial efforts to maintain neutrality, public opinion in the United States began to shift in favor of entering the war. The sinking of the Lusitania and other civilian ships, the Zimmerman Telegram, and the perceived threat to American interests and safety created a groundswell of support for intervention.
5. Influence of Allies: The Allied powers, particularly Britain and France, engaged in diplomatic efforts to persuade the United States to join their cause. They presented arguments based on the principles of democracy, freedom, and the need to counter German militarism. These appeals resonated with Wilson's own ideals and values.
6. Russian Revolution: The collapse of the Russian monarchy in February 1917 and the subsequent Bolshevik Revolution in October shifted the geopolitical landscape. Wilson saw an opportunity to establish a more stable and democratic government in Russia, which aligned with his vision for a postwar world based on self-determination and collective security.
In light of these factors, Wilson reluctantly concluded that the United States could no longer remain neutral and delivered his historic address to Congress on April 2, 1917, asking for a declaration of war against Germany. The US officially entered World War I on April 6, 1917.