| 140041 | December 12 | Event | 627 – Battle of Nineveh: A Byzantine army under Emperor Heraclius defeats Emperor Khosrau II's Persian forces, commanded by General Rhahzadh. |
| 140042 | December 12 | Event | 1098 – First Crusade: Siege of Ma'arrat al-Numan – Crusaders breach the town's walls and massacre about 20,000 inhabitants. After finding themselves with insufficient food, they reportedly resort to cannibalism. |
| 140043 | December 12 | Event | 1388 – Mary of Enghien sells the lordship of Argos and Nauplia to the Republic of Venice. |
| 140044 | December 12 | Event | 1408 – The Order of the Dragon a monarchical chivalric order is created by Sigismund of Luxembourg, then King of Hungary. |
| 140045 | December 12 | Event | 1781 – American Revolutionary War: Second Battle of Ushant – A British fleet led by HMS Victory defeats a French fleet. |
| 140046 | December 12 | Event | 1787 – Pennsylvania becomes the second state to ratify the United States Constitution, five days after Delaware became the first. |
| 140047 | December 12 | Event | 1862 – American Civil War: USS Cairo sinks on the Yazoo River, becoming the first armored ship to be sunk by an electrically detonated mine. |
| 140048 | December 12 | Event | 1870 – Joseph H. Rainey of South Carolina becomes the second black U.S. congressman, the first being Hiram Revels. |
| 140049 | December 12 | Event | 1897 – Belo Horizonte, the first planned city in Brazil, is founded. |
| 140050 | December 12 | Event | 1901 – Guglielmo Marconi receives the first transatlantic radio signal (the letter "S" [***] in Morse Code), at Signal Hill in St John's, Newfoundland. |
| 140051 | December 12 | Event | 1911 – Delhi replaces Calcutta as the capital of India. |
| 140052 | December 12 | Event | 1911 – King George V of the United Kingdom and Mary of Teck are enthroned as Emperor and Empress of India. |
| 140053 | December 12 | Event | 1915 – President of the Republic of China, Yuan Shikai, announces his intention to reinstate the monarchy and proclaim himself Emperor of China. |
| 140054 | December 12 | Event | 1917 – In Nebraska, Father Edward J. Flanagan founds Boys Town as a farm village for wayward boys. |
| 140055 | December 12 | Event | 1918 – The Flag of Estonia is raised atop the Pikk Hermann for the first time. |
| 140056 | December 12 | Event | 1925 – The Majlis of Iran votes to crown Reza Khan as the new Shah of Iran, starting the Pahlavi dynasty. |
| 140057 | December 12 | Event | 1935 – Lebensborn Project, a Nazi reproduction program, is founded by Heinrich Himmler. |
| 140058 | December 12 | Event | 1936 – Xi'an Incident: The Generalissimo of the Republic of China, Chiang Kai-shek, is kidnapped by Zhang Xueliang. |
| 140059 | December 12 | Event | 1937 – Second Sino-Japanese War: USS Panay incident – Japanese aircraft bomb and sink U.S. gunboat USS Panay on the Yangtze river in China. |
| 140060 | December 12 | Event | 1939 – Winter War: Battle of Tolvajärvi – Finnish forces defeat those of the Soviet Union in their first major victory of the conflict. |
| 140061 | December 12 | Event | 1939 – HMS Duchess sinks after a collision with HMS Barham off the coast of Scotland with the loss of 124 men. |
| 140062 | December 12 | Event | 1940 – World War II: Approximately 70 people are killed in the Marples Hotel, Fitzalan Square, Sheffield, as a result of a German air raid. |
| 140063 | December 12 | Event | 1941 – World War II: Fifty-four Japanese A6M Zero fighters raid Batangas Field, Philippines. Jesús Villamor and four Filipino fighter pilots fend them off César Basa is killed. |
| 140064 | December 12 | Event | 1941 – World War II: USMC F4F "Wildcats" sink the first 4 major Japanese ships off Wake Island. |
| 140065 | December 12 | Event | 1941 – World War II: The United Kingdom declares war on Bulgaria. Hungary and Romania declare war on the United States. India declares war on Japan. |
| 140066 | December 12 | Event | 1941 – Adolf Hitler declares the imminent extermination of the Jews at a meeting in the Reich Chancellery |
| 140067 | December 12 | Event | 1942 – World War II: German troops begin Operation Winter Storm, an attempt to relieve encircled Axis forces during the Battle of Stalingrad. |
| 140068 | December 12 | Event | 1942 – A fire in a hostel in St. John's, Newfoundland, kills 100 people. |
| 140069 | December 12 | Event | 1946 – A fire at a New York City ice plant spreads to a nearby tenement, killing 37 people. |
| 140070 | December 12 | Event | 1948 – Malayan Emergency: Batang Kali massacre – 14 members of the Scots Guards stationed in Malaya allegedly massacre 24 unarmed civilians and set fire to the village. |