Macbeth took the throne after killing his cousin, King Duncan I, in battle in 1040. In 1046, Siward, earl of Northumbria, unsuccessfully attempted to dethrone Macbeth in favor of Malcolm. In 1054, Macbeth was apparently forced by Siward to yield part of southern Scotland to Malcolm. Three years later, Macbeth was killed in battle by Malcolm, with assistance from the English.