what roles did the sinking of the Lusitania and the Zimmerman Note play in bringing the United States into World War 1?

The sinking of the Lusitania and the Zimmerman Note play a part in bringing the United States into World War 1 because it is showed that Germany was posed as a threat to the United States. The sinking of the Lusitania reveals that Germany defied the policy of unrestricted submarine warfares, which caused 128 American passengers to die. The Zimmerman Note disclosed that Germany had the idea of forming an alliance with Mexico.