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.

What's the best answer to this question: was the us part of world war 1?
yes