February 24 - World War I: United States ambassador to the United Kingdom Walter H. Page is given the Zimmermann Telegram, in which Germany offers to give the American Southwest back to Mexico if Mexico will declare war on the United States.
March 2 - The enactment of the Jones Act grants Puerto Ricans United States citizenship.
March 21 - The Danish West Indies become the Virgin Islands when Denmark transfers control over the islands to the United States after the purchase of the islands on January 25.
March 26 - World War I: Battle of Gaza - British cavalry troops retreat after 17,000 Turks block their advance.
March 31 - The United States takes possession of the Virgin Islands after paying $25 million to Denmark.
December 6 - Halifax explosion: A ship collision in the harbour at Halifax, Nova Scotia causes a huge explosion that kills more than 1900 people and destroys part of the city. Until Hiroshima, this was the biggest manmade explosion.