For the first three years of World War I, the [[United States]] attempted to stay out of the war, but try to act as a mediator. Mediation failed. When the Germans used a [[U-boat]] to sink the British ocean liner ''[[Lusitania]]'' in 1915, killing over one thousand civilians including some prominent Americans, the Americans were outraged. Badly hurt by the British naval blockade of Germany, which cut off food supplies, the Germans wanted to retaliate. In early 1917 they decided they could defeat Britain and France by cutting off all supplies. They could only do this by sinking merchant ships without warning, which violated international law and their repeated promises to the U.S. Berlin knew it meant war with the U.S. but moved anyway. At the same time Berlin invited Mexico to form a military alliance and fight the U.S. Publication of the [[Zimmerman Telegram]] was a ''casus bellum" (cause of war). The Mexicans wisely ignored the proposal but American pubic opinion was outraged. | For the first three years of World War I, the [[United States]] attempted to stay out of the war, but try to act as a mediator. Mediation failed. When the Germans used a [[U-boat]] to sink the British ocean liner ''[[Lusitania]]'' in 1915, killing over one thousand civilians including some prominent Americans, the Americans were outraged. Badly hurt by the British naval blockade of Germany, which cut off food supplies, the Germans wanted to retaliate. In early 1917 they decided they could defeat Britain and France by cutting off all supplies. They could only do this by sinking merchant ships without warning, which violated international law and their repeated promises to the U.S. Berlin knew it meant war with the U.S. but moved anyway. At the same time Berlin invited Mexico to form a military alliance and fight the U.S. Publication of the [[Zimmerman Telegram]] was a ''casus bellum" (cause of war). The Mexicans wisely ignored the proposal but American pubic opinion was outraged. |