She was designated Henry's heir, and on his death (1135), Stephen seized the throne and Matilda invaded England (1139) inaugurating a period of inconclusive civil war. She and her second husband (Geoffrey) captured Normandy and in 1152 the Treaty of Wallingford recognized Henry as Stephen's heir. Burke says she was betrothed in her eighth year (1119) to Henry.

Civil war with Stephen of Blois, who was crowned King, although he had taken an oath to see her as Queen of England.

Because her father's 2d marriage was childless, at Christmas 1126 he designated his daughter, the widowed Empress Matilda, as his successor and the following May he chose a 2d husband for her, the young and handsome Geoffrey, son of the Count of Anjou, who was 10 years or more her junior.

From "Debrett's Kings and Queens of Britain" by David Williamson, ISBN 0-86350-101-X, p. 50-51:
Matilda's first cousin, Stephen of Blois, was such a weak and ineffective character that it is a wonder how he attained the crown. He was the 3rd son of Adela, the strong-minded daughter of the Conqueror. In 1126 Stephen was the first of the lay barons to swear to acknowledge his cousin, the Empress Matilda, as heiress to England and Normandy. He again swore fealty on the birth of her son Henry in 1133. In spite of these solemn oaths, on the death of his uncle, Stephen left his county of Boulogne, but a day's journey from southeast England, and went straight to London where he secured the support of the citizens. He was crowned on St Stephen's Day 1135 by William de Corbeil, Archbishop of Canterbury.
His cousin Matilda protested against Stephen's succession but he was recognized by Pope Innocent II. Baronial insurrections and wars with the Scots, terminating in Stephen's victory at the Battle of the Standard occupied the early years of the reign.
Empress Matilda landed in England in the autumn of 1139, where she was ably supported by her half-brother Robert, Earl of Gloucester, and was joined by several powerful barons.
In the course of the civil wars which ensued, Stephen was captured at Lincoln in Feb 1141 and imprisoned at Bristol. His brother, Bishop Henry, turned against him and a legatine council of the English Church held at Winchester declared Stephen deposed and proclaimed Matilda "Lady of the English" on 7 Apr 1141.
Stephen's supporters continued the struggle and, having managed to capture Robert of Gloucester, exchanged him for Stephen, who had himself re-crowned on the anniversary of his first coronation. This was still not an end to the strife which ravaged the country, Stephen and Matilda alternately gaining the upper hand.
In 1144 Stephen lost Normandy to Geoffrey of Anjou, Matilda's 2d husband. A feud with the papacy led to an interdict in 1148, not raised until 1151. In 1152 Stephen sought to secure the succession in his own family by crowning his son, Eustace, a practice in use in France, but the Pope refused to sanction it. Matilda by this time had retired to Normandy, but her son Henry, now grown to manhood, took her place in 1153 and was joined by all her old supporters. This time the matter was settled without further bloodshed and by the Treaty of Westminster it was agreed that Stephen should retain the crown for life and that Henry should succeed him.

She retained a great influence on her son, King Henry II until her death in 1167, and she had taken care with his education and he was well-grounded in law and history.