America stays home

January 1917. Germany is about to resume unrestricted submarine warfare, and its foreign secretary, Arthur Zimmermann, prepares an insurance policy. On 16 January he cables Mexico an offer: join Germany if America enters the war, and recover Texas, New Mexico and Arizona. To reach Washington, the telegram travels routes the British can tap, including, absurdly, the American diplomatic cable itself. In Room 40 of the Admiralty, Britain's codebreakers read it within days. Admiral Hall stages the reveal to hide his sources, the telegram is published on 1 March, and Zimmermann confirms it is genuine. Five weeks later the United States declares war.

In the timeline recorded here, the insurance policy stays in its drawer. Berlin's ambassador in Washington, Bernstorff, refuses to pass a war plot down the American government's own wire. He has spent two years keeping America neutral, and he will not burn his work in one cable. The message waits for a safer route, and then for a better moment, and the moment never comes. In Room 40 the green lamps burn over other men's traffic. The telegraph blank that would have moved a nation is never filled in, and February arrives with the submarines and nothing else.