| 91081 | August 12 | Event | 1164 – Battle of Harim: Nur ad-Din Zangi defeats the Crusader armies of the County of Tripoli and the Principality of Antioch. |
| 91082 | August 12 | Event | 1323 – Signature of the Treaty of Nöteborg between Sweden and Novgorod (Russia), that regulates the border between the two countries for the first time. |
| 91083 | August 12 | Event | 1499 – First engagement of the Battle of Zonchio between Venetian and Ottoman fleets. |
| 91084 | August 12 | Event | 1624 – The president of Louis XIII of France's royal council is arrested, leaving Cardinal Richelieu in the role of the King's principal minister. |
| 91085 | August 12 | Event | 1676 – Praying Indian John Alderman shoots and kills Metacomet, the Wampanoag war chief, ending King Philip's War. |
| 91086 | August 12 | Event | 1687 – Battle of Mohács: Charles of Lorraine defeats the Ottoman Empire. |
| 91087 | August 12 | Event | 1765 – Treaty of Allahabad is signed. The Treaty marks the political and constitutional involvement and the beginning of Company rule in India. |
| 91088 | August 12 | Event | 1793 – The Rhône and Loire départments are created when the former département of Rhône-et-Loire is split into two. |
| 91089 | August 12 | Event | 1806 – Santiago de Liniers, 1st Count of Buenos Aires re-takes the city of Buenos Aires, Argentina after the first British invasion. |
| 91090 | August 12 | Event | 1831 – French intervention forces William I of the Netherlands to abandon his attempt to suppress the Belgian Revolution. |
| 91091 | August 12 | Event | 1851 – Isaac Singer is granted a patent for his sewing machine. |
| 91092 | August 12 | Event | 1877 – Asaph Hall discovers the Mars moon Deimos. |
| 91093 | August 12 | Event | 1883 – The last quagga dies at the Artis Magistra zoo in Amsterdam, Netherlands. |
| 91094 | August 12 | Event | 1898 – An Armistice ends the Spanish–American War. |
| 91095 | August 12 | Event | 1898 – The Hawaiian flag is lowered from ʻIolani Palace in an elaborate annexation ceremony and replaced with the flag of the United States to signify the transfer of sovereignty from the Republic of Hawaii to the United States. |
| 91096 | August 12 | Event | 1914 – World War I: The United Kingdom declares war on Austria-Hungary the countries of the British Empire follow suit. |
| 91097 | August 12 | Event | 1914 – World War I: The Battle of Haelen a.k.a. (Battle of the Silver Helmets) a clash between large Belgian and German cavalry formations at Halen, Belgium. |
| 91098 | August 12 | Event | 1944 – Waffen-SS troops massacre 560 people in Sant'Anna di Stazzema. |
| 91099 | August 12 | Event | 1944 – Nazi German troops end the week-long Wola massacre, during which time at least 40,000 people were killed indiscriminately or in mass executions. |
| 91100 | August 12 | Event | 1944 – Alençon is liberated by General Philippe Leclerc de Hauteclocque, the first city in France to be liberated from the Nazis by French forces. |
| 91101 | August 12 | Event | 1947 – United Nations Security Council Resolution 29 relating to UN membership of Yemen and Pakistan is adopted. |
| 91102 | August 12 | Event | 1948 – USS Nevada is struck from the naval record. |
| 91103 | August 12 | Event | 1950 – Korean War: Bloody Gulch massacre—American POWs are massacred by North Korean Army. |
| 91104 | August 12 | Event | 1952 – The Night of the Murdered Poets: Thirteen prominent Jewish intellectuals are murdered in Moscow, Russia, Soviet Union. |
| 91105 | August 12 | Event | 1953 – Nuclear weapons testing: The Soviet atomic bomb project continues with the detonation of Joe 4, the first Soviet thermonuclear weapon. |
| 91106 | August 12 | Event | 1953 – The islands of Zakynthos and Kefalonia in Greece are severely damaged by an earthquake measuring 7.3 on the Richter scale. |
| 91107 | August 12 | Event | 1958 – Art Kane photographs 57 notable jazz musicians in the black and white group portrait "A Great Day in Harlem" in front of a Brownstone in New York City. |
| 91108 | August 12 | Event | 1960 – Echo 1A, NASA's first successful communications satellite, is launched. |
| 91109 | August 12 | Event | 1964 – South Africa is banned from the Olympic Games due to the country's racist policies. |
| 91110 | August 12 | Event | 1964 – Charlie Wilson, one of the Great Train Robbers, escapes from Winson Green Prison in Birmingham, England, United Kingdom. |