Final answer:
The correct answer is option 1. In January 1917, Germany announced the resumption of unrestricted submarine warfare, abandoning the Sussex Pledge and targeting any ship in declared war zones, which led to tension with neutral countries like the United States and influenced the U.S. decision to enter World War I.
Step-by-step explanation:
In January 1917, Germany announced that it would resume unrestricted submarine warfare, a critical decision in World War I. This policy meant that German submarines (U-boats) would engage in the sinking of enemy and neutral ships without warning in the waters around Great Britain and the Western Front. The Sussex Pledge, which had been a commitment made by Germany to the United States in 1916 to limit submarine warfare and avert provoking the U.S. into entering the war, was consequently set aside.
The resumption of unrestricted submarine warfare was a calculated risk by Germany, which hoped to starve Britain into submission before the United States could effectively intervene in the war. Despite observing the limitations of the U.S. military in conflicts like with Pancho Villa, Germany underestimated the speed and force with which the U.S. could mobilize for war. This aggressive naval policy contributed to the severing of diplomatic ties between the United States and Germany and played a significant role in the U.S. decision to join the Allied forces against Germany later that year.