The United States declared war on Germany on April 6, 1917, over 2 years after World War I started. A ceasefire and Armistice was declared on November 11, 1918. Before entering the war, the U.S. had remained neutral, though it had been an important supplier to Great Britain and the other Allied powers.

Based on this passage, who did america fight with in world war 1? Let's think fast. Stream of consciousness:
To answer the question, consider the following: The United States declared war on Germany on April 6, 1917, over 2 years after World War I started. So the final answer is Germany.