The document summarizes America's entry into World War I from neutrality to declaring war in April 1917. Key events that pushed the US into the war included the sinking of American ships by German U-boats, especially the Lusitania disaster, and the Zimmerman Telegram, which proposed a German alliance with Mexico if the US entered the war. Over 2 million American troops were deployed to Europe led by General Pershing, tipping the balance in favor of the Allies, though they faced modern weapons and hazardous conditions in trench warfare.