After the death of Henry, however, the political situation in England became less stable, with both Stephen of England and the Empress Matilda laying claim to the throne. Brien had originally been considered a supporter of Stephen, but in 1139 Matilda travelled to England and Brien announced his allegiance to her, joining forces with Miles of Gloucester and other supporters in the south-west. Wallingford Castle was now the most easterly stronghold of the Empress's faction – it was either the closest base to London, or the first in line to be attacked by Stephen's forces, depending on one's perspective.