The State Department instructs the U.S. Ambassador in Mexico to inform the Mexican government that the United States knows about the Zimmermann Telegram. Department counselor Frank Polk discusses the...

U.S. Ambassador Walter H. Page is provided a translation of the telegram on Feb. 23 and informed of Germany’s proposal to Mexico by British Foreign Secretary Arthur Balfour. On Feb. 24, Ambassador...

Heinrich von Eckardt, the German envoy to Mexico, discusses the telegram with Mexican foreign minister Cándido Aguilar.

The British decode the intercepted message and discover the German proposal for an alliance with Mexico against the United States.

The U.S. troops of the Punitive Expedition, after skirmishes with Carrancistas forces and successful diplomacy, withdraw from Mexico.

United States severs diplomatic relations with Germany. President Woodrow Wilson tells a joint session of Congress that Germany’s policy of unrestricted U-boat warfare poses an unacceptable threat to ...

The United States is informed of the German High Command order to resume unrestricted submarine warfare.

Germany’s foreign minister, Arthur Zimmermann, cables the coded proposal to Germany’s Ambassador in Washington D.C., Count Johann Henrich von Bernstorff. Because of severed transatlantic lines,...

A proposal of an alliance with Mexico is drafted by Hans Arthur von Kemnitz, a German foreign office official.

Having suspended attacks in 1916 to avoid U.S. entry into the war, German officials decide to re-engage in unrestricted submarine warfare against all ships.