In pre-Columbian times, what is now Argentina comprised a diversity of native peoples who ranged from small isolated bands of hunter-gatherers to semiurbanized outliers of Inka Cusco (in present-day Perú ). The Inka were never quite able to impose their will on the agricultural Diaguita peoples, who exercised autonomy in what are now Salta, Tucumán, La Rioja Catamarca, and San Juan Province s.
Likewise, the Inka had little control over the southerly Araucanians—the semisedentary Mapuche and the closely related Pehuenche and Puelche—who withstood both the Inka expansion and, for more than three centuries, the Spanish invasion. More numerous on the Chilean side of the Andes, they survived because of distance from Cusco, their mobility as shifting cultivators, and their decentralized political structure—not easily conquered or co-opted by the bureaucratic Inka. Likewise, the decentralized Guaraní of Mesopotamia  were a more or less independent people.
In Patagonia, groups like the Chonos, Tehuelche (Aónikenk), Kawésqar (Alacaluf), Yámana (Yahgan), and Selk’nam (Ona) subsisted by hunting, fishing, and gathering, but introduced European diseases and outright extermination devastated their already small numbers, and sheep displaced the guanaco and rhea on which many of them relied.
At the time of the Spanish invasion, the Inka ruled a centralized but unwieldy empire; their hold was especially tenuous on the southern Araucanian (Mapuche) frontier, just as it would be for the Spaniards in just a few years. Though Inka political achievements were impressive, their realm having stretched into present-day Colombia in the north, they were relative latecomers in the pre-Columbian Andes, only consolidating their power around A.D. 1438. Building on earlier Andean advances in mathematics, astronomy, and other sciences, they were a literate and administratively sophisticated society, but their hierarchical organization, like that of the modern Soviet Union, was ultimately unsustainable.
Toward the end of the 15th century, just prior to the Spanish invasion of the New World, the Inka empire was no monolith, but rather a diverse realm with a mosaic of peoples who resisted domination, especially on its most remote frontiers. Because of internal divisions after the premature deaths of the Inka ruler Huayna Capac and his immediate heir, there developed a struggle between potential successors Atahualpa and Huáscar. That the Inka state was a house divided against itself helps explain why a relatively small contingent of Spanish invaders could overcome vastly superior numbers, but it’s only part of the story.