The Anarchy in English history commonly names the period of civil war and unsettled government that occurred during the reign (1135–1154) of King Stephen of England. Stephen was a favourite nephew of King Henry I of England (reigned 1100–1135), whose only legitimate son died in 1120 in the "White Ship" disaster. Henry then named his daughter Matilda as heir to his throne. He forced his barons, including Stephen, to swear allegiance to her several times, but it went against the grain—no woman had ever ruled over all England in her own right. To make matters worse, Matilda had married Geoffrey of Anjou, who did not enjoy a good reputation in England. This was mainly because he hailed from Anjou, whose rulers were resented by the Normans for their unashamed attempts to conquer the duchy of Normandy.
On Henry's death in 1135, Stephen rushed to England. Despite the fact that the barons already seemed to be leaning towards the election of his elder brother, Theobald, who was Count of Blois, with great speed he entered London and was elected king by the townspeople, who saw it as their ancient right to decide upon the king. From here he moved to Winchester, where, with the support of his younger brother Henry, who was the bishop, he secured the treasury and the support of both the archbishop William Corbeil, and the Chief Justiciar, Roger of Salisbury. The barons preferred Stephen to Matilda and so ratified the usurpation, the main opposition coming from Matilda's illegitimate half-brother, Robert of Gloucester, who never supported Stephen whole-heartedly since he, Robert, was the half brother of Matilda and thus the main rival to Stephen in terms of landed wealth. The Archbishop of Canterbury and Pope Innocent II sided with Stephen. Matilda's best hope, her uncle, King David I of Scotland, invaded Northumberland, nominally on her behalf. Little actual fighting took place, but Thurstan, Archbishop of York, won the Battle of the Standard on Stephen's behalf in August 1138.
Later in the same year, Robert of Gloucester changed sides and allied himself with Matilda, also known as the Empress Maud. Stephen, meanwhile, made a series of poor decisions that caused resentment amongst his former supporters. His own brother, Henry, Bishop of Winchester, turned against him due to his arrest of prominent bishops in the land, which Henry perceived as an attack on the church itself, and in 1139, Matilda entered England and made a stand at Arundel Castle. Stephen allowed her to travel to Bristol to meet up with Robert of Gloucester, in order to try to contain any enemies in one area. Another prominent opposing earl, Ranulf of Chester, had moved to Lincoln and proceeded to capture the castle. Despite making apparent peace with Ranulf, Stephen responded to a plea from the citizens of Lincoln to attack the castle he held. Ranulf got wind of this, and managed to escape and muster a force of knights, in conjunction with his father-in-law, Robert of Gloucester. Thus the stage was set for battle. In the only major battle of the struggle, Stephen suffered defeat on February 2, 1141. He was made a prisoner at Bristol, and Matilda temporarily ruled from London. However, her haughty manner soon made her enemies there, and she felt obliged to leave the capital for Oxford. In September of 1141, Robert of Gloucester fell into enemy hands following the rout of Winchester at the hands of Stephen's wife, Matilda of Boulogne, and his mercenary captain, William of Ypres. Matilda decided to get Robert back via an exchange for Stephen, who returned to the throne. He now held most of the country and besieged Matilda at Oxford Castle. Her escape by night in the snow to Wallingford has become legendary.
Unrest continued throughout Stephen's reign, even after Matilda had returned to Anjou following Robert's death in 1147. The Peterborough Chronicle offers an eye-witness account of the civil war and its suffering. According to its author, Stephen was a "softe and gode" man who "no iustice didde," and "Crist and alle his sayntes slept". These things, and "mare thanne we cunnen sæin, we tholeden xix wintre for ure sinnes" ("more than we can say, we suffered 19 winters for our sins"). It is because of the lack of rule, the lack of security, and the lack of safety that the era is referred to as "the Anarchy."
Stephen himself was in poor health by this time, and he suffered a further blow when his eldest son, Eustace, died suddenly in 1153 — Stephen had wanted Eustace crowned during his own lifetime, but the Pope had refused to allow it and even put England under an interdict for a time during the squabble. Matilda's son, the future Henry II of England, had by now grown up into a skilled military tactician and a determined opponent, and he arrived in England with the intention of conquest. By the Treaty of Winchester (also known as the Treaty of Wallingford), which the two men signed in November 1153, Stephen recognised Henry as heir to the throne. The rumours which for years had been circulating that Stephen was Henry II's biological father were reinforced by his agreement to let Henry succeed him although he had another surviving son (William of Blois), but no evidence supporting that story has ever emerged. Matilda never ruled in her own right.