B. The expulsion of non-Christians from Spain.
The Reconquista had the ultimate effect of driving Muslims out of the Iberian Peninsula, and contributed to the unification of a single Spanish kingdom.
Muslim incursions into the Iberian Peninsula had happened already back in the 8th century, and Muslim populations controlled the southern portions of Spain and Portugal for many centuries. "The Reconquista" is the name given to the retaking of the lands by Portugal and Spain, completed in 1492. Following that, there were efforts to force Muslims to convert to Catholic Christianity if they wished to remain in the land. [Jews were targeted also.] The Reconquista had been pursued on and off since the 8th century, but was most aggressively--and successfully--carried out by the monarchy team of Ferdinand and Isabella, who completed the conquest over Muslims in Grenada in 1492.
Ferdinand of Aragon and Isabella of Castile had joined their kingdoms by marriage to one another in 1469. Their success against the Muslim presence in the peninsula advanced their control over all of Spain. Under their son, King Charles I, Spain was ruled as a single kingdom. (Charles is perhaps more famously known also as Holy Roman Emperor Charles V, as he held that imperial title also from 1519 to 1556.)
