Who was the stalemate in world war 1 broken by?

The stalemate in World War I was broken primarily by the entry of the United States into the war in 1917. The influx of American troops and resources provided a significant boost to the Allied forces. Additionally, new military tactics and technologies, such as tanks and improved artillery, helped to break the deadlock on the Western Front. Ultimately, these factors contributed to the eventual defeat of the Central Powers in 1918.