What event finally caused President Wilson to ask for a decloration of war against Germany?

President Wilson asked for a declaration of war against Germany primarily in response to unrestricted submarine warfare, particularly after the sinking of the British ocean liner RMS Lusitania in 1915, which resulted in the deaths of American passengers. However, the final catalyst was the revelation of the Zimmermann Telegram in early 1917, in which Germany proposed a military alliance with Mexico against the United States. These provocations, combined with Germany's continued aggression, led Wilson to seek a formal declaration of war on April 2, 1917.