The Zimmermann Telegram was an intercepted diplomatic communication from German Foreign Secretary Arthur Zimmermann to the German ambassador in Mexico, proposing a military alliance: Germany would help Mexico recover Texas, New Mexico, and Arizona from the United States if Mexico would declare war on the U.S. The telegram was intercepted and decoded by British intelligence. The textbook describes its publication in 1917 as “undoubtedly the most important propaganda achievement of the British” — the British had been conducting covert propaganda in the U.S. to build support for the Allied cause, and the Zimmermann revelation dramatically shifted American public opinion. It helped persuade President Wilson and the U.S. Congress to declare war on Germany, bringing America into WWI on the Allied side. This is a classic example of intelligence-based propaganda — using real (but strategically timed and framed) information as a propaganda weapon.