Answer: Germany started a total submarine war.
Step-by-step explanation:
After Germany started a total submarine war, some American prodigies were killed. In this way, Germany violated the agreement with the United States on neutrality. Apart from this reason, there are also economic factors that brought the United States into the war. Britain and France bought large quantities of weapons from the United States. There was a possibility that France and Great Britain would lose the war not to repay the debt to the United States.