Final answer:
At the time of the Spanish invasion, the Americas' Indigenous peoples were in a period that succeeded the Paleo-Indian, Archaic, and Woodland periods, characterized by advanced development including the agricultural revolution with the Mesoamerican Triad as a staple.
Step-by-step explanation:
When the Spaniards invaded the Americas, the Indigenous peoples of the Americas were in a period that had evolved from the earlier Paleo-Indian period, lasting until about 8,000 BCE when humans were nomadic hunter/gatherers. The native cultures further developed and diversified during subsequent periods known as the Archaic (8,000-1,000 BCE) and the Woodland periods (1,000 BCE -1,000 CE). During these eras, especially notable is the beginning of the domestication of plants and the development of agriculture, highlighted by the cultivation of crops such as corn, beans, and squash, forming the Mesoamerican Triad, a critical contribution to agricultural diets. By the time of the Spanish invasion following Columbus' discovery, indigenous societies had been established for many centuries and were subject to dramatic changes and declines in population due to the conquest leading to the spread of European diseases and the imposition of colonial rule.