Catholicism and the Crown
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The first step taken by the unified kingdoms of Aragon and Castile was to defeat the Moorish kingdoms in the south of the Iberian Peninsula, which were Muslim kingdoms. This placed a large number of both Muslims and Jews residing in those kingdoms under control of the Spanish monarchs, who were devout Christians. Spanish rulers began pushing for religious uniformity in their lands, which meant expulsions or forced conversions for the non-Christian population. The Spanish Inquisition was formed to investigate claims that converts did not truly abandon their previous fate. Spanish culture also took on a more Christian overtone, inspired by the hardening religious beliefs of both the monarchy and the Spanish citizens.