For broader historical context, see 13th century.
- The first Shepherds' Crusade, a domestic French uprising in response to events in Egypt during the Seventh Crusade, occurs.
- King Alexander III of Scotland marries Margaret, daughter of King Henry III of England, precipitating a power struggle between the two monarchs.
- 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.
Mindaugas of Lithuania is baptized, in prelude to his crowning as King of Lithuania in 1253.
Alexander Nevsky signs the first peace treaty between Kievan Rus' and Norway.
- King Conrad IV of Germany invades Italy, but fails to subdue the supporters of Pope Innocent IV.
- The German city of Berlin, founded some fifty years earlier, receives its city charter.
Otakar II of Bohemia, later to become King of Bohemia, is elected Duke of Austria.
- The earliest known manuscript of The Proverbs of Alfred, a collection of sayings of England's Alfred the Great, is written.
List of state leaders in 1251