Woodrow Wilson was the US President during WWI. Tensions in Europe led to war in 1914 due to militarism, alliances, imperialism, and nationalism. The assassination of Archduke Franz Ferdinand of Austria-Hungary by Serbian nationalists triggered Austria-Hungary to declare war on Serbia and drew other European powers into the growing conflict. While the US aimed to remain neutral, events like the sinking of passenger liners like the Lusitania by German U-boats and the Zimmerman Telegram drew the US into the war on the side of the Allies in 1917.