The Spanish conquest of the Inca Empire, also known as the Conquest of Peru, was one of the most important campaigns in the Spanish colonization of the Americas. After years of preliminary exploration and military skirmishes, 168 Spanish soldiers under conquistador Francisco Pizarro, his brothers, and their indigenous allies captured the Sapa Inca Atahualpa in the 1532 Battle of Cajamarca. It was the first step in a long campaign that took decades of fighting but ended in Spanish victory in 1572 and colonization of the region as the Viceroyalty of Peru. The conquest of the Inca Empire (called "Tahuantinsuyu" or "Tawantinsuyu" in Quechua, meaning "Realm of the Four Parts"), led to spin-off campaigns into present-day Chile and Colombia, as well as expeditions to the Amazon Basin and surrounding rainforest. When the Spanish arrived at the borders of the Inca Empire in 1528, it spanned a considerable area and was by far the largest of the four grand pre-Columbian civilizations. Extending southward from the Ancomayo, which is now known as the Patía River, in southern present-day Colombia to the Maule River in what would later be known as Chile, and eastward from the Pacific Ocean to the edge of the Amazonian jungles, it covered some of the most mountainous terrains on Earth. In less than a century, the Inca had expanded their empire from about in 1448 to in 1528, just before the arrival of the Spanish. This vast area of land varied greatly in culture and climate. Because of the diverse cultures and geography, the Inca allowed many areas of the empire to be governed under the control of local leaders, who were watched and monitored by Inca officials. Under the administrative mechanisms established by the Inca, all parts of the empire answered to, and were ultimately under the direct control of, the Inca Emperor. Scholars estimate that the population of the Inca Empire was more than 16,000,000. Some scholars, such as Jared Diamond, believe that while the Spanish conquest was undoubtedly the proximate cause of the collapse of the Inca Empire, it may very well have been past its peak and already in the process of decline. In 1528, Emperor Huayna Capac ruled the Inca Empire. He could trace his lineage back to a "stranger king" named Manco Cápac, the mythical founder of the Inca clan, who, according to tradition, emerged from a cave in a region called Paqariq