It entered British history when Henry became bishop of Winchester and his brother set aside Matilda for the throne.  
The decline of this family became irreversible when the countship passed to the House of Chatillon.  The zenith of its power was reached when it was combined with Champagne under the leadership of Eudes II.  Founded by Thibaut the Cheat, its hereditary dominion extended from the Indre River to the Eure.  It entered British history when Henry became bishop of Winchester and his brother set aside Matilda for the throne.  FTP, name the short-lived English royal house of King Stephen.
The decline of this family became irreversible when the countship passed to the House of Chatillon.  
Blois