ver 116,000 U.S. citizens died in World War I, making it the third bloodiest war in U.S. history behind World War II and the U.S. Civil War. Though the reasons for the United States’ entry into World War I are many, one of the primary reasons was the Zimmerman telegram, a communique sent from Germany to Mexico, but intercepted and deciphered by British code breakers. The Zimmerman telegram threatened the U.S. territories, thus shifting public sentiment in favor of the Allied Powers of Great Britain, France and Russia.