European societies around 1492 were characterized by rigid social hierarchies with the powerful Catholic Church. The Crusades weakened the Church's authority and nobility while sparking increased trade. By the 1400s, population growth and trade with Asia created wealth in Europe. Monarchs gained power by collecting taxes and raising armies, allowing them to pursue exploration for economic and political reasons. Advances in shipbuilding and navigation enabled Portugal and Spain to take the lead in exploration, ushering in widespread changes epitomized by Columbus' voyages, including the Columbian Exchange of plants, animals and disease, and the beginning of the transatlantic slave trade.