Complex sentence: 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 Stephen's brother, Henry of Blois, Bishop of Winchester.
Split into simpler sentences: Henry's attempts to install his daughter, the Empress Matilda, as his successor were unsuccessful. On Henry's death in 1135, his nephew Stephen of Blois seized the throne with the help of Stephen's brother, Henry of Blois, Bishop of Winchester.