World War I/United States

Reasons for U.S. Involvement in World War I

 * German submarine warfare; especially the sinking of the Lusitania by a German U-boat.
 * The United States had economic and political ties to Great Britain
 * The Zimmerman Telegram
 * Inability to remain neutral

Zimmerman Telegram
The Zimmerman Telegram was sent from Germany to Mexico in 1917. It asked Mexico to join the Central Powers and attack the United States. Mexico refused to attack the U.S., but when the U.S. found out about the Zimmerman Telegram, it angered Americans and led to the U.S. declaring war on Germany.

Lusitania Sinking
The RMS Lusitania was a British ocean liner that was sunk by a torpedo from a German U-boat in 1915. 128 Americans on board were killed. This event angered many Americans, but the U.S. would remain neutral until Woodrow Wilson led the nation to war in 1917.