Answer: the USA entered World War I because Germany had sunk a ship with US passengers, the Lusitania, after an agreement that neither would attack in the sea warzone.
Another factor that caused the USA to enter World War I was the Zimmerman Telegram, Germany sent a coded telegram to Mexico in hopes of getting Mexico to ally with them and turn against the USA.
Answer:In early 1917 Berlin forced the issue. Its declared decision on 31 January 1917 to target neutral shipping in a designated war-zone became the immediate cause of the entry of the United States into the war. Five American merchant ships went down in March.
