<P> Spain colonized and exerted control of Alta California through the Spanish missions in California until the Mexican secularization act of 1833 . </P> <P> In 1532 at the Battle of Cajamarca a group of Spaniards under Francisco Pizarro and their indigenous Andean Indian auxiliaries native allies ambushed and captured the Emperor Atahualpa of the Inca Empire . It was the first step in a long campaign that took decades of fighting to subdue the mightiest empire in the Americas . In the following years Spain extended its rule over the Empire of the Inca civilization . </P> <P> The Spanish took advantage of a recent civil war between the factions of the two brothers Emperor Atahualpa and Huáscar, and the enmity of indigenous nations the Incas had subjugated, such as the Huancas, Chachapoyas, and Cañaris . In the following years the conquistadors and indigenous allies extended control over Greater Andes Region . The Viceroyalty of Perú was established in 1542 . The last Inca stronghold was conquered by the Spanish in 1572 . </P> <P> European explorers arrived in Río de la Plata in 1516 . Their first Spanish settlement in this zone was the Fort of Sancti Spiritu established in 1527 next to the Paraná River . Buenos Aires, a permanent colony, was established in 1536 and in 1537 Asunción was established in the area that is now Paraguay . Buenos Aires suffered attacks by the indigenous peoples that forced the settlers away, and in 1541 the site was abandoned . A second (and permanent) settlement was established in 1580 by Juan de Garay, who arrived by sailing down the Paraná River from Asunción (now the capital of Paraguay). He dubbed the settlement "Santísima Trinidad" and its port became "Puerto de Santa María de los Buenos Aires ." The city came to be the head of the Governorate of the Río de la Plata and in 1776 elevated to be the capital of the new Viceroyalty of the Río de la Plata . </P>

According to the text what motivated the spaniards and conquistadors to explore the americas