The Incas assimilated a huge chunk of western South America, concentrated on the Andean Mountains, from 1438 to 1533, employing conquest and peaceful absorption, among other tactics. Their dominion extended over most of present-day Peru and parts of Chile, Ecuador, Bolivia, and Argentina.
That's more than 150 years! Even if we assume that they lost every single battle they fought (which is unlikely since they were capable of repeatedly defeating larger armies), their existence as a nation would have been short. They would have been conquered by one aggressive enemy or another, probably in less than 100 years.
In fact, the last Inca emperor, Huayna Capac, was only 16 when he took the throne in 1529; his brother, Charles I, then aged 19, became his co-ruler two years later. The first Spanish ambassador to arrive in Peru was told that there were no longer any kings in that country; instead, there were only princes who ruled their subjects well enough to keep them loyal. This was probably an accurate description of the situation during Huayna Capac's brief reign.
The empire was already in decline when it was taken over by the Spaniards in 1532.
From the 1400s until the arrival of the Spanish in 1532, the Inca Empire was centered in Peru and reigned over much of South America's west coast. The Incas built roads, canals, and cities, and they also practiced human sacrifice. The ideology behind the Inca civilization was based on the belief that the earth was created by a supreme creator god who then took three children from each tribe to live in heaven. When he died, God became man so that he could learn what it was like to be human. Every part of his body was used as a tool by which he learned how to create. He is called "Inca" because he taught the people many things, including farming, architecture, engineering, and science. The Incas invented a writing system that included pictures of plants and animals that could not speak. They also developed a counting system that included numbers up to 20.
Because the Incas believed that the world was created by a god, they did not destroy their environment or kill humans like other civilizations have done before and after them. The Spaniards thought that the Incas were the most powerful nation in South America and said that they ruled over more than 150,000 subjects. In fact, the Incas only controlled about one-third of what is now Peru.
1532 Two lucky conditions assist the Spaniards march into the Inca empire in 1532. One is that the kingdom is in disarray due to civil conflict between two brothers, the sons of an Inca ruler who died roughly five years ago. The other is that the king is away in southern Peru dealing with a rebellion. Without him to control the territory, there is no one to defend the cities against attack. When the Inca king returned home, he found his country destroyed and his people enslaved. He quickly agreed to peace terms which included handing over all his subjects for punishment by Spanish judges. However, many indigenous people refused to surrender and were killed or forced into slavery.
1540's The first expedition led by Francisco Pizarro arrives at the city of Lima where they are welcomed by the governor who gives them land to build their town. This is because the emperor who rules over the entire continent is too busy fighting wars to care about what happens to any one group. He orders the governors of different provinces to provide security for travelers and trade goods while he fights off rebels.
1550's A second expedition led by Hernando de Soto travels south into unexplored territory looking for gold. They find only Indians who have never seen anyone like them before. After killing some of them and taking their slaves, the Spaniards continue on their journey with nothing to show for their effort but huge debts.
On the other hand, nothing came close to the size of the Inca Empire, and they innovated in a number of ways. For example, they relocated a sizable portion of the population—somewhere in the three million range, maybe as many as five million. They did this by building large cities with straight, well-kept roads that were used by the government for tax collection and war efforts.
The Incas had a large population, but also high rates of mortality from disease and violence. The Spanish historians who wrote about the Incas estimated that their death rate was about one in ten, which means that about ninety percent of them lived.
The Incas built hundreds of miles of paved roads across their empire. These roads were used by the government for tax collection and military campaigns. The largest of these cities was Incarí in what is now Peru, where researchers have found evidence of up to two hundred thousand people living in huge blocks surrounded by walls over nine feet tall and twenty-five feet wide.
Incarí was abandoned before the Spanish arrived in Peru, which shows how important it was to the Incas that they survived disease and violence.
People often say that the Incas' ideas didn't live long enough to be copied, but this isn't true.