The events of March 1917 which resulted in President Woodrow Wilson summoning a special session of Congress to declare war are told in this latest post from US blogger Dennis Cross. Here's his summary:
'It's the last month of neutrality for the United States and the last month of his reign for the Tsar of All the Russias. In the United States, publication of the Zimmermann Telegram triggers a political firestorm. Pacifists and isolationists at first denounce it as a forgery perpetrated by Great Britain, but Zimmermann himself acknowledges authorship and American public opinion begins to swing in favor of war. The House of Representatives passes the Armed Ships Bill, and seventy-five senators sign a manifesto in support, but a filibuster prevents it from coming to a vote. President Wilson denounces the filibusterers as “a little group of willful men, representing no opinion but their own,” and orders that merchant ships be armed anyway. The Senate adopts its first rule limiting debate. Three American merchant ships are sunk by German submarines; twelve Americans die. The Federal Reserve Board revises its advice to member banks: loans to the Allies are now encouraged. The Cabinet unanimously recommends declaring war on Germany, and President Wilson calls Congress into special session. In Russia, Army mutinies and demonstrations in the streets of Petrograd force Tsar Nicholas II to abdicate; he is taken into custody and replaced by a Provisional Government. Vladimir Lenin and Leon Trotsky set out for Russia, Lenin from Switzerland and Trotsky from New York. In Mesopotamia, the British Army occupies Baghdad. Alexandre Ribot succeeds Aristide Briand as Prime Minister of France. The inventor of the Zeppelin dies.'
Read the full post here.