Why did the usa get involved?
The United States entered WW1 with the sinking of their ship, Lusitania, in 1917. Prior to 1915, German subs had a policy of warning and allowing time to evacuate ships carrying passengers before they sank them. However, in 1915 the Lusitania was sunk without a warning, killing over 120 Americans. One year later, the Sussex was sunk by German U-boats and American citizens were outraged at these direct violations of their neutral rights at sea. At this point, a small percentage of Americans, including president Teddy Roosevelt, demanded "immediate warfare." In 1916 President Wilson took a stronger stance toward foreign affairs by increasing the size of the military and issuing a warning to the Germans. The Germans complied for a while but then eventually decided to go back to submarine warfare. After, Foreign Minister Alfred Zimmerman attempted to provoke Mexico and Japan into attacking the United States with the promise of German assistance after the European front was conquered. A message containing Zimmerman's intent was decoded by the British and sent to the US, further swaying Americans to action.
The picture on the left shows a main reason on why the United States entered World War I. It depicts the sinking of the Lusitania and the Americans attempting to escape.