Peru and neighboring countries
the time of contact with the Spanish in 1532 the Inca Empire was
comparable in size to the Roman Empire. It stretched from northern Peru
and Equador in the north to Bolivia in the south, east into the Amazon
jungle and along the western coast. It was a vast and well administered
theocracy with the Inca ruler as leader. Yet it was only a few years
before a few hundred Spanish Conquistadors would topple the Empire and
turn it into a Spanish colony. How was this possible?
This region of South America had been inhabited since at least 3000 BC. The civilization previous to the Inca was the Tiwanaku culture centered around Lake Titicaca to the south. Some theorize that Inca stonework is based on similar techniques developed by the Tiwanaku. The Tiwanaku culture faded away around 900-1000 BC.
It has long been theorized that the Inca Empire came to dominate the region around the middle of the 15th century at the end of a war with the Chanca tribe to the north and that all of the conquest of territory, the creation of the networks of roads, and the building of temples, towns, and cities occurred in the following 100 years prior to European contact. This seems a bit implausible until you visit the sites at which point it becomes laughable. Clearly there is more to the history of the Empire than a 100 year reign. Unfortunately there are no written records prior to the Spanish because the Inca had no written language. Theories are the best we can do.
A much more reasonable hypothesis is that the civilization later to be the Inca Empire was in place and maturing slowly and peacefully (more or less) in the Cuzco area for several centuries before the great war with the Chancas. Gradually there was a consolidation and centralization of power in Cuzco. The period of 1100 -1400 AD was one of regional economic trade and not necessarily conflict. Around the middle of the 15th century the Inca Empire as we perceive it developed out of this widepsread but well developed economic activity and the Empire of the Four Corners, Tawantinsuyu, was born.
The leader at the time of the Chanca war was Pachacuteq, "Transformer of the Earth". He divided the Empire into four zones with Cuzco at the center. To the north was Chinchaysuyu in northern Peru and Equador, south was Collasuyu in the high plains of southern Peru and Bolivia. To the east was Antisuyu in the Amazon jungle and west was Contisuyuof the southern coasts. Whether accurate or not, his reign is credited with most of the large building programs that we still see today. Regardless, his reign began the Inca Empire we have come to accept, but within one hundred years that Empire would fall before the Spanish Conquistadors.
In 1532 as the Spanish led by Francisco Pizzarro were arriving in Peru, a terrible civil war was raging within the Empire. A power struggle between two brothers over leadership of the Empire had weakened the once strong civilization. Atawallpa from the northern region was challenging Huascar of the Cuzco region. Atawallpa would dominate, later capturing Hauscar near Cuzco. Atawallpa might have reunited the Empire had it not been for the arrival of the Spanish. When they arrived they sided with the Cuzco faction, capturing Atawallpa, and ransoming him for a room filled with gold (as legend states). They later executed him and replaced him with a puppet Inca, Manco II, a half brother of Hauscar. Manco escaped and in 1536 returned to lead an army against the Spanish nearly defeating them. As the Spanish were providing written accounts of the events, we have at least their version of what took place. Many battles and several great sieges took place including a repulsing of the Spanish at Ollantaytambo and near defeat during the siege at Sacsaywaman. There is a good deal of information available about the fall of the Inca Empire under the Spanish if you are interested.