What two German actions caused the United States to enter World War I?

Sinking of the British-Liner Ship Lusitania: While the claim that the British were transporting war-material & equipment was true, the US was outraged, for the ship sank with 128 American lives abroad. This led to public shift from being neutral towards the Allied side in significant numbers.

The Zimmerman Telegram: The Zimmerman Telegram was sent from the Zimmerman of Germany to Mexico in an effort to have Mexico to join the Central side. In return Germany would later help Mexico retake all lands they lost to the U.S. during the Texas Independence and Mexican-American war.