What was used by the monarchs to unify Spain under Christianity and consolidate their power.

Catholic Monarchs, also called Catholic Kings, or Catholic Majesties, Spanish Reyes Católicos, Ferdinand II of Aragon and Isabella I of Castile, whose marriage (1469) led to the unification of Spain, of which they were the first monarchs. Although employed earlier, the appellation Católicos was formally conferred on them in a bull published by Pope Alexander VI in 1494, in recognition of their reconquest of Granada from the Moors (1481–92), their New World discoveries (1492), and their strengthening of the church by such agencies as the Spanish Inquisition and such measures as compelling Jews to convert to Christianity or face exile (1492). The title of Católicos was afterward transmitted to the successors of Ferdinand and Isabella.

Explanation:

b) the importance and limits of political power.