In 1916 Woodrow Wilson was elected to a second term as president primarily on his strong reputation as a peacemaker. But just one year later America would enter the most brutal and bloody conflict the world had ever yet known. Wilson led the country into World War I.

What changed in America? A single Western Union telegram, composed and sent in code from German Foreign Minister Arthur Zimmermann to the government of Mexico was intercepted and deciphered by British cryptographers. The contents outraged Americans and changed the national mood from peace to war.

Ironically this is precisely what Germany was trying to avoid. After the British set up an effective Naval blockade, the Germans responded by breaking the Sussex Pledge that bound them to limit submarine warfare. Instead they adopted a policy of unrestricted warfare and began attacking unarmed civilian vessels.

This was an effective if brutal tactic, but it came with one potentially game-changing side effect. It might draw the United States, until then a neutral observer, into the war. And indeed the Americans severed ties with Germany.

To mitigate the possibility of direct US military involvement, German foreign minister Arthur Zimmermann sent a regular Western Union telegram to Mexico. Written in code, Zimmermann's missive asked the Mexicans to enter the conflict, if the United States did, and to recruit Japan too. In exchange for this he promised financial aid and the return of "conquered" Mexican territories Texas, New Mexico and Arizona.

Mexico and Japan never entered the war. But the United States did. And that's how a single, decrypted telegram assured Germany's defeat and changed the history of the world.

A testament to the power decryption in propaganda the museum features a copy of the New York Tribune of March 1, 1917, complete with screaming headline: "Germany asked Mexico to unite with Japan in war on United States." The telegram and, especially, the headlines propelled America into World War I.

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