What happened when Germany renewed submarine warfare in 1917?

When Germany renewed unrestricted submarine warfare in 1917, it aimed to cut off supplies to the Allies by targeting merchant ships, including those from neutral countries. This aggressive strategy heightened tensions with the United States, which had previously maintained a neutral stance. The sinking of ships like the Lusitania and increased American casualties ultimately contributed to the U.S. entering World War I in April 1917, shifting the balance in favor of the Allies.