Final answer:
Monarchs used religious conversion and persecution, typified by the Reconquista and the Inquisition, to unify Spain under Christianity and consolidate their power, alongside economic development and the strengthening of the church's socio-economic role. (option C)
Step-by-step explanation:
The monarchs used religious conversion and persecution to unify Spain under Christianity and consolidate their power. When Ferdinand and Isabella took the throne, they began a process known as the Reconquista, aimed at retaking Iberian territories from Muslim control, culminating in the capture of Granada in 1492. This effort continued with the establishment of the Inquisition, which forced Muslims and Jews to either convert to Catholicism or leave Spain. The monarchs had a two-pronged approach to securing their reign: they reduced the power of the nobility to fortify royal control and relied on the church’s influence to enforce religious conformity.
During this time, the Roman Catholic Church grew in power and landholdings, contributing to Spain's economic and social structures being deeply intertwined with religious institutions. The church's involvement in trade and agriculture, as well as the expansion of guilds and city councils, helped stimulate economic development in Spain. Moreover, the push for religious uniformity was also carried to the New World, where Spanish monarchs oversaw the conversion of indigenous populations to Christianity.