What are 2 factors that caused the United states to enter war?

Two significant factors that caused the United States to enter World War I were unrestricted submarine warfare by Germany and the interception of the Zimmermann Telegram. Germany's aggressive submarine tactics threatened American shipping and lives, particularly after the sinking of the Lusitania. The Zimmermann Telegram, which revealed Germany's proposal to Mexico for a military alliance against the U.S., further inflamed public opinion and pushed the U.S. government towards war.