When the War began in 1914, the United States took a neutrality stance and continued to trade with the countries on both sides of the conflict. Although very quickly the Germans began to implement their war policy of Unrestricted submarine warfare. Where they would use U-Boats to attack a ship that wasn’t German which included ships with American civilians inside. This caused the sinking of British ship Lusitania which was a civilian ship was shot down by German U-Boats and the ship was carrying 128 American.
This caused Woodrow Wilson the American president at the time to send a strongly worded letter to Kaiser Wilhelm the leader of Germany at the time. This lead to strict regulation on the use of U-Boat to the point that it wasn’t worth using. This lasted about two years but then the military higher-ups convinced the government to reinstate the U-Boat attacks, which they did.
Later on, during the war, Germany decided to reinstate the U-Boat attacks saying that it was not worth the disadvantage they got while fighting just to please the United States. Saying We have been challenged to fight to the end. We accept the challenge. We stake everything, and we shall be victorious. This increased tensions between Germany and the United States and it pushed the US closer to the Triple Entente. What pushed them over the cliff was when they offered to help mexico take over the land that the US had taken from them in the past. The message was intercepted by Britain and they relayed the information to the US ambassador in London.
This was considered unacceptable and US president Woodrow Wilson asked congress to give him permission to join the war. Soon after the Germans lost the war, this was maybe the biggest mistake they made during the war!