The most accurate summary of the United States’ involvement and military role in World War I among the given options is:
The U.S. became involved in World War I after the Zimmermann Telegram, and sent troops to provide military reinforcements and support.
This statement accurately reflects the significant factors leading to U.S. involvement, including the Zimmermann Telegram, which was a secret communication from Germany to Mexico proposing a military alliance against the U.S., and the subsequent decision to send American troops to assist the Allies in 1917.