The Oxford Parliament, led by Simon de Montfort, 6th Earl of Leicester, leads to the acceptance by King Henry III of England of the Provisions of Oxford.
September - The Empire of Nicaea defeats the Principality of Achaea at the Battle of Pelagonia, ensuring the eventual reconquest of Constantinople in 1261.
August 11 - While conducting a siege against the Song Dynasty city known as Fishing Town in the province of Chongqing, China, the Mongol Khagan, Mongke Khan, dies in the nearby hills. Persian, Chinese, and Mongol records have different accounts of how he died, including succumbing to an arrow wound received by a Chinese archer in the siege, dysentery, and even cholera epidemic. His death sparks a succession crisis in the Mongol Empire, while his brothers Ariq Böke and Kublai soon convene their own kuriltai to elect themselves as the next Khan of Khans, opening the path to a four year long civil war from 1260 to 1264. In the end, Ariq Böke surrendered to Kublai.
While engaged in a war with the Mongols, the Song Chinese official Li Zengbo wrote in his Kozhai Zagao, Xugaohou that the city of Qingzhou was manufacturing one to two thousand strong iron-cased gunpowder bomb shells a month, dispatching to Xiangyang and Yingzhou about ten to twenty thousand such bombs at a time.
Lannathai, a kingdom in the north of Thailand, is founded by King Mengrai.
The Goryeo kingdom in Korea surrenders to invading Mongol forces.
The Chinese era Kaiqing begins and ends in the Northern Song Dynasty of China.
The Japanese Shōka era ends, and the Shōgen era begins.
