December 1917

December – Annie Besant becomes president of the Indian National Congress.

December 3 – After nearly 20 years of planning and construction, the Quebec Bridge opens to traffic (the bridge partially collapsed on August 29, 1907 and September 11, 1916). 

December 6 - The Senate of Finland officially declares the country's independence from Russia.
   
Halifax Explosion: Two freighters collide in Halifax Harbour at Halifax, Nova Scotia and cause a huge explosion that kills at least 1,963 people, injures 9,000 and destroys part of the city (the biggest man-made explosion in recorded history until the Trinity nuclear test in 1945). 

December 9 – WWI: The British Egyptian Expeditionary Force accepts the surrender of Jerusalem by the mayor, Hussein al-Husayni, following effective defeat of the Ottoman Empire's Yildirim Army Group during the Battle of Jerusalem.

December 11 – WWI: General Edmund Allenby leads units of the British Egyptian Expeditionary Force into Jerusalem on foot through the Jaffa Gate.

December 17 – The Raad van Vlaanderen proclaims the independence of Flanders.

December 20 – The Cheka, a predecessor to the KGB is established in Russia.

December 25 – Jesse Lynch Williams' Why Marry?, the first dramatic play to win a Pulitzer Prize, opens at the Astor Theatre in New York.

December 26 – United States president Woodrow Wilson uses the Federal Possession and Control Act to place most U.S. railroads under the United States Railroad Administration, hoping to transport troops and materials for the war effort more efficiently.

December 30 – WWI: Egyptian Expeditionary Force secures the victory at the Battle of Jerusalem by successfully defending Jerusalem from numerous Yildirim Army Group counterattacks.