The 1250s was a decade perhaps most dominated by the Mongols, who under the leadership of Möngke Khan continued their rapid expansion throughout Asia both to the east and west of their home territories. The Mongols destroyed the Kingdom of Dali in Laos, and captured the Goryeo kingdom in Korea, Galicia in eastern Europe, Anatolia in Turkey, and the Islamic center of Baghdad, where over 80,000 are killed as the city was burned to the ground. In Thailand the Lannathai kingdom was founded. In Japan, a new sect of Buddhism was formed, while in Korea the carving of Buddhist scriptures on 81,000 wooden blocks was completed.
Europe noted several important cultural milestones, including the completion of several important cathedrals and the beginning of construction of others, as well as the founding of the Collège de Sorbonne at the University of Paris. Significant political developments in Europe included the lack of a Holy Roman Emperor for most of the decade, further erosion of the power of the monarchy in England and Portugal, the end of the failed Seventh Crusade in Egypt, and the expulsion of the Jews from France and the Moors from Portugal. In religion, a papal bull authorized the use of torture in the Medieval Inquisition, and the Catholic church clarified the concept of purgatory. Several important modern cities, including Stockholm and Lviv, were founded in the 1250s.
1256 - Hulagu Khan establishes the Ilkhanate dynasty of Persia, which will become one of four main divisions of the Mongol Empire.
1258 - February 10 - The Hulagu Khan's Mongol forces overrun Baghdad, then the leading center of Islamic culture and learning, burning it to the ground and killing as many as 800,000 citizens.
1259 - The Goryeo kingdom in Korea surrenders to invading Mongol forces.
1251 - Andrew of Longumeau , dispatched two years earlier by King Louis IX of France as an ambassador to the Mongols, returns to his king with reports from the Mongols and Tartary; his mission is considered a failure.
1254 - King Louis IX of France expels all Jews from France.
1254 - King Afonso III of Portugal holds the first session of the Cortes (Portugal's general assembly composed of nobles, members of the middle class, and representatives from all municipalities) in Leiria.
1254 - In England, an important step in the evolution of the Parliament and Peerage occurs, as lesser barons are replaced on the King's Council by elected representatives from shires and cities.