I wanted to make sure that this is correct. Please give me your input. Thanks a lot!!

Question

The countries involved in World War I was Russia, France, Italy, and Britain, Germany, Austria-Hungary, the Ottoman Empire, and Bulgaria. I think Mexico was also but not sure.

Germany’s actions were causing the U.S. to become aggravated and disturbed. Two main factors that led the U.S. to be involved in the war were discovering the alliance between Mexico and Germany. (Why did the U.S. become angry?)Between February 3 and March 21 German-boats sank six American merchant ships without warning. In April 2, 1917 declared war on Germany

How did the U.S enter the war?