During the conflict, John II, in the face of French aggression in the Pyrenees "had his heir Ferdinand married to Isabella I of Castile, the heiress to the Castilian throne, in a bid to find outside allies" (Balcells 11). Their dynastic union, which came to be known as the Catholic Monarchs, marked the "de facto" unification of the Kingdom of Spain. At that point, however, "de jure" both the Castile and the Crown of Aragon remained distinct territories, each keeping its own traditional institutions, parliaments and laws. This was a common practice at this time in Western Europe as the concept of sovereignty lay with the monarch.