How did the German policy of unrestricted submarine warfare affect the us?

The German policy of unrestricted submarine warfare, initiated in early 1917, significantly impacted the United States by leading to the sinking of civilian and merchant ships, including the RMS Lusitania, which resulted in American casualties. This aggressive tactic heightened tensions between Germany and the U.S., ultimately contributing to the U.S. decision to enter World War I in April 1917. The policy galvanized public opinion against Germany and underscored the need for a robust U.S. response to protect its interests and citizens on the high seas.