On October 27, 939, Edmund I becomes King of the English following the death of his half-brother Æthelstan. Edmund's reign as monarch saw much warfare with the invasion of Northumbria and the Midlands by King Olaf III Guthfrithson and the Edmund's reconquest of said territories in 942 following the death of Olaf. Edmund also conquered Strathclyde and used it to negotiate a treaty of mutual military support with King Malcolm I of Scotland in 945. Despite such successes, his reign was short-lived. Edmund I was killed on May 26, 946, by an exiled robber. Edmund I was succeeded first by his brother Eadred followed by his sons Eadwig and Edgar the Peaceful.