What was responsible for turning America public opinion against Germany?

There were a number of factors that contributed to the United States' changing public opinion against Germany during the First World War. These included:

- The sinking of the Lusitania: In 1915, a German U-boat sank the British passenger liner RMS Lusitania, killing 1,198 people, including 128 Americans. This event caused a great deal of anger and resentment in the United States, and many people began to believe that Germany was waging an indiscriminate and brutal war.

- The Zimmerman Telegram: In 1917, the British intercepted and decoded a telegram from German Foreign Secretary Arthur Zimmermann to the German ambassador in Mexico. The telegram proposed an alliance between Germany and Mexico, in which Mexico would attack the United States in return for German support in regaining territory lost in the Mexican-American War. The telegram was leaked to the press, and it further inflamed public opinion against Germany.

- The unrestricted submarine warfare: Germany's decision to wage unrestricted submarine warfare against all ships, including those of neutral countries, also angered many Americans. Unrestricted submarine warfare resulted in the sinking of several American merchant ships, and it led to the deaths of hundreds of American citizens.

- Propaganda: Both the German and American governments engaged in extensive propaganda campaigns during the war. The German government sought to portray itself as the victim of aggression, while the American government sought to portray Germany as a ruthless and barbaric enemy. These propaganda campaigns helped to shape public opinion in both countries.

By 1917, public opinion in the United States was overwhelmingly in favor of entering the war against Germany. The United States declared war on Germany on April 6, 1917.