Obviously, Spain had its hands full in the Americas in the early 16th century, but why didn't they decide to also continue the Reconquista into Morocco, especially once they started getting flooded with New World gold and silver? Just a case where they recognized that they'd be overextended?
Edit: Inspired by the trope that if the Americas hadn't been discovered in 1492, Spain would have poured all its resources into a North African invasion.
Edit: Inspired by the trope that if the Americas hadn't been discovered in 1492, Spain would have poured all its resources into a North African invasion.