- Jan 1 1st first blood transfusion using stored and cooled blood is performed
- Jan 1 1st issue of "Journal of Negro History" published
- Jan 1 2nd Rose Bowl, Tournament Park, Pasadena, California: Washington State beats Brown, 14-0; MVP: Carl Dietz, Washington State
- Jan 5 Austria-Hungary offensive against Montenegro
Germany to Abide Maritime Warfare Rules
Jan 7 In response to pressure from President Woodrow Wilson, Germany notifies the US State Department that it will abide by strict international rules of maritime warfare
Gallipoli: Guts, Glory and Defeat
Jan 9 The Ottoman Empire prevails in the Battle of Çanakkale, as the last British troops evacuated
- Jan 10 In retaliation for President Woodrow Wilson's recognition of Mexico's Carranza government, members of Pancho Villa's revolutionary army take 17 US mining engineers from a train and shoot 16 of them in cold blood
- Jan 10 Russian offensive in Caucasus
- Jan 11 Austrian forces capture Mount Lovćen, Serbia. Serbian army retreats, evacuating to Greek island of Corfu
- Jan 12 Britain proclaims Gilbert & Ellice Islands as a colony in Pacific
- Jan 12 Max Immelmann and Oswald Boelcke receive the Pour le Merite, the German Empire's highest military award, for achieving eight aerial victories each over Allied aircraft
- Jan 14 Dutch Zuiderzee dyke cracks
- Jan 17 Rodman Wanamaker organises a lunch to discuss forming a golfers association (later the PGA) at the Taplow Club, Martinique Hotel, New York City
- Jan 18 A 611 gram chondrite type meteorite stikes a house near the village of Baxter in Stone County, Missouri
- Jan 23 Temperature falls from 44°F (7°C) to -56°F (49°C) night of 23-24, Browning, Montana
- Jan 24 The Military Service Bill, calling for conscription of men for war services, passes in the British House of Commons
- Jan 25 Montenegro surrenders to Austria-Hungary
- Jan 27 Communist party "Spartacus Letters" 1st published in Berlin
- Jan 28 German colony of Cameroon surrenders to Britain & France
- Jan 28 Manitoba women are the first in Canada to win the right to vote and to hold provincial office [1]
- Jan 28 Opera "Goyescas" premieres in New York City
- Jan 28 US President Woodrow Wilson nominates Louis Brandeis for the Supreme Court of the United States
- Jan 29 1st bombing of Paris by German Zeppelins takes place
- Jan 31 Dutch Girl Guides form
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