The statement that best summarizes the United States' involvement and military role in World War I is:
The U.S. became involved in World War I after the Zimmermann Telegram, and sent troops to provide military reinforcements and support.
While several factors, including unrestricted submarine warfare by Germany and other provocations, contributed to U.S. entry into the war in 1917, the Zimmermann Telegram was a significant catalyst that helped sway public opinion and government decision-making toward declaring war on Germany. The United States did indeed send troops to provide military support and reinforcements to the Allies after formally entering the war in April 1917.