Period 1: Contact, Exchange, and Colonization, 1491–1607
Many worlds before contact
Native North America before 1492 was not a single world but many: Pueblo farmers of the Southwest with irrigation and adobe towns; Plains peoples whose bison economy later expanded with horses; Mississippian mound-builders at Cahokia; Eastern Woodland confederacies such as the Iroquois, with matrilineal clan politics. Questions often test the link between environment and social organization, so learn two or three specific examples in detail rather than a generic 'Native American' label.
Exchange and empire
The Columbian Exchange is the central concept of the period: crops, animals, and people moved in both directions, but the decisive transfer was disease. Smallpox and other pathogens killed the vast majority of indigenous people, destroying labor systems and destabilizing empires. Spanish colonization rested on the encomienda (forced labor grants), missions, and a casta hierarchy that ranked people by ancestry. French traders built alliances and fur-trade networks with relatively few settlers; the Dutch pursued commerce along the Hudson; English colonization began with Roanoke's failure and Jamestown's 1607 founding.
Traps: do not credit Columbus with discovering a hemisphere, do not treat the exchange as only beneficial, and do not confuse encomienda with chattel slavery. Periodize carefully-1607 is a boundary, so the Pueblo Revolt (1680) belongs to Period 2.
Worked example: if asked what most explains the rapid collapse of the Aztec and Inca states, choose epidemic disease plus indigenous allies and internal division, not simply Spanish firearms.
Rule of thumb: motives predict institutions-gold and conversion produced extractive Spanish labor systems, fur trade produced French alliance and intermarriage, and settler agriculture produced English land seizure.