Pre-Columbian civilizations in the Americas developed complex societies with advanced agriculture, architecture, and astronomy. The Olmec, Maya, Aztec, and Inca empires thrived, creating impressive cities and sophisticated cultural systems before European arrival. European exploration, led by Columbus, sparked a dramatic transformation of the Americas. Spanish conquistadors conquered indigenous empires, while diseases decimated native populations. The Columbian Exchange reshaped ecosystems and economies on both sides of the Atlantic.