Before the arrival of Europeans, native populations in North America developed diverse social, political, and economic structures based on their environments and interactions. The three major civilizations were the Mayans, Aztecs, and Incas, who practiced advanced agriculture, built large cities, and developed complex societies. European expansion starting in the 15th century resulted in the Columbian Exchange and drastic population changes on both sides of the Atlantic. The Spanish established large empires in Central and South America but oppressed native populations, while other European powers like England began exploring North America in search of resources and new markets. Contact between Europeans, Africans, and Americans challenged the worldviews of all groups.