When World War I—at the time called the Great War—broke out in the summer of 1914, President Woodrow Wilson was determined to remain neutral and keep the United States out of the conflict. However, following the sinking of the passenger liner Lusitania, which was torpedoed by a German U-boat and resulted in the deaths of 128 Americans, and the interception of the Zimmermann telegram revealing Germany’s plan to back Mexico if that country declared war on the United States, President Wilson was forced to react. The United States declared war on Germany on April 6, 1917. The United States’ entry into the war is seen as ushering in the end of the Progressive Era.