 The Kingdom of Castile had been prosperous and successful in Europe thanks in part to the unusual authority and control the king exerted over the nobility, which ensured political stability and kept the kingdom from being weakened by in-fighting (as was the case in England, for example).However, under the Trastámara dynasty, both kings of Castile and Aragon had lost power to the great nobles, who now formed dissenting and conspiratorial factions.Taxation and varying privileges differed from county to county, and powerful noble families constantly extorted the kings to attain further concessions, particularly in Aragon.