Henry of Blois in the context of Wolvesey Castle

The Anarchy was a civil war in England and Normandy between 1138 and 1153 which resulted in a widespread breakdown in law and order. The conflict was a war of succession precipitated by the accidental death of William Adelin—the only legitimate son of King Henry I—who drowned in the White Ship disaster of 1120. Henry sought to be succeeded by his daughter, Empress Matilda, but was only partially successful in convincing the nobility to support her. On Henry's death in 1135, his nephew Stephen of Blois seized the throne with the help of his brother Henry of Blois, who was the bishop of Winchester. King Stephen's early reign saw fierce fighting with disloyal English barons, rebellious Welsh leaders, and Scottish invaders. Following a major rebellion in the southwest of England, Matilda invaded in 1139 with the help of her half-brother Robert of Gloucester.

In the initial years of civil war, neither side achieved a decisive advantage; Matilda came to control southwest England and much of the Thames Valley, while Stephen remained in control of the southeast. Barons who refused to support either side held much of the country. The castles of the period were easily defensible, so the fighting was mostly attrition warfare comprising sieges, raiding and skirmishing. Armies mainly consisted of knights and infantry, many of them mercenaries. In 1141 Stephen was captured following the Battle of Lincoln, causing a collapse in his authority over most of the country. When Matilda attempted to be crowned queen, she was forced instead to retreat from London by hostile crowds; shortly afterwards, Robert of Gloucester was captured by Stephen's wife, Matilda of Boulogne, at the rout of Winchester. The two sides agreed to a prisoner exchange, swapping the captives Stephen and Robert. Stephen then almost captured Matilda in 1142 during the Siege of Oxford, but she escaped from Oxford Castle across the frozen Thames to safety.

In the Rout of Winchester (14 September 1141) the army of imprisoned King Stephen of England, led by his wife, Queen Matilda of Boulogne, Stephen's brother Bishop Henry of Blois, and William of Ypres, faced the army of Stephen's cousin Empress Matilda, whose forces were commanded by her half-brother Earl Robert of Gloucester. After Empress Matilda's army besieged a castle on the edge of Winchester, Queen Matilda's army arrived and blockaded the Angevin army within the city. Cut off from supplies, the Angevin army gave up the siege, then was crushed as it began to retreat. Robert of Gloucester was captured and was subsequently exchanged for Stephen, who was returned to the throne of England. However, the civil war known as The Anarchy dragged on with neither side gaining an advantage.