- Dec 1 Boys Town founded by Father Edward Flanagan west of Omaha, Nebraska
- Dec 2 Han Yong-woon, found Zen awakening at Osean Monastery Korea
- Dec 3 After nearly 20 years of planning and construction, the Quebec Bridge finally opens to traffic after two prior collapses
- Dec 3 The Supreme Allied War Council, meeting at Versailles to define war aim, fails to reach an agreement
- Dec 5 Austro-German Forces launch an offensive against the Italians on the western end of their line, around Asiago
- Dec 6 French munition ship SS Mont Blanc collides with Norwegian SS Imo in Halifax harbour, Canada, resulting explosion kills at least 1,700 and injures more than 9,000 people - world’s largest pre-atomic explosion [1]
- Dec 6 Taking advantage of the temporary relaxation of authority in Russia, Finland declares itself a republic, following the Ukraine on 20 November
US's 42nd Rainbow Division
Dec 7 The USA's 42nd 'Rainbow' Division arrives in France (with Colonel Douglas MacArthur among its ranks)
- Dec 7 US becomes 13th country to declare war on Austria during World War I
- Dec 9 British forces under General Allenby capture Jerusalem
- Dec 11 13 black soldiers hanged for participation in Houston riot
- Dec 11 German-occupied Lithuania proclaims independence from Russia
- Dec 12 French troop train derails in French Alps killing 543
- Dec 12 Rev Edward Flanagan forms Boys Town outside Omaha, Nebraska
- Dec 14 UFA, Universal Film AG, forms in Germany
- Dec 15 Moldavian Republic declares independence from Russia
- Dec 15 World War I: An armistice is reached between the new Russian Bolshevik government and the Central Powers
Prohibition Passes
Dec 18 The 18th Amendment to the US Constitution, authorizing prohibition of alcohol, is approved by the US congress and sent to the states for ratification [1]
Finnish Independence Recognized
Dec 18 The Soviet government issues a decree recognizing Finland's newly-declared independence [N.S. December 31]
- Dec 19 1st NHL game played on artificial ice in Toronto
- Dec 19 Quebec Bulldogs play their 1st professional hockey game
- Dec 20 A second nationwide referendum on military conscription is rejected by the Australian public
- Dec 20 Soviet state security force and forerunner to the KGB, the Cheka forms, under Felix Dzerzhinsky after decree by Vladimir Lenin
- Dec 22 Flanders declares its independence, under Pieter Tack
- Dec 22 In the NHL's first official week of play, 3 players score hat tricks in the same game, for the same team; Corb Denneny, Reg Noble, & Harry Meeking each score 3 for the Toronto Arenas in an 11-4 win over the Ottawa Senators
- Dec 23 3 British warships come close to Holland
- Dec 25 "Why Marry" 1st drama to win Pulitzer Prize, premieres in NYC
- Dec 25 Louis Hirsch and Otto Harbach's musical "Going Up" premieres in New York City
- Dec 26 1st NHL defensemen to score a goal: Toronto Maple Leaf Harry Cameron
- Dec 26 US Federal government took over operation of American railroads for duration of WW I
- Dec 30 -32°F (-36°C) in Mountain City, Tennessee (state record)
- Dec 30 -37°F (-38°C) in Lewisburg, WV (state record)
- Dec 31 Dutch Social-democratic trade union NVV counts 159,450 members
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