America Joins the War
Already angry about the German submarine attacks, America finds out that Germany is plotting with Mexico against them...
In February 1917 a note was given to the US ambassador in Britain. The note contained a message that had been sent in secret by Germany to Mexico. It was captured and decoded by British intelligence. The message was shocking. Germany wanted Mexico to agree to an alliance if America came into the war. In return Germany would give Mexico money and help them to invade America and occupy some of the southern states. The message is called the Zimmerman Telegram - named after the man who wrote it, Germany's Foreign Secretary Arthur Zimmerman.
...so the USA joins the war on 6th April.
This was the last straw for President Wilson. First Germany had introduced unrestricted submarine warfare and American ships had been sunk. Now Germany was directly threatening America by plotting with Mexico.
On 2nd April 1917 President Wilson made a speech to Congress - the American version of the Houses of Parliament. He said that Germany's actions were the same as declaration of war against America. Congress agreed and on 6th April 1917 America declared war on Germany.
In May 1917 the United States passed a law allowing men aged 21-30 to be selected to fight. This was called the draft. Here a blindfolded man picks out numbers at random. The numbers each represent a man.