The Anarchy was a civil war in England and Normandy between 1135 and 1154, which resulted in a widespread breakdown in law and order. The conflict was a succession crisis precipitated by the accidental death of William Adelin, only legitimate son of Henry I, in 1120. Henry's attempts to install his daughter, the Empress Matilda, as his successor were unsuccessful and on Henry's death in 1135, his nephew Stephen of Blois seized the throne with the help of another nephew, Henry of Blois, Bishop of Winchester. Stephen's early reign was marked by fierce fighting with English barons, rebellious Welsh leaders and Scottish invaders. Following a major rebellion in the south-west of England, Matilda invaded in 1139 with the help of her half-brother, Robert of Gloucester.