The Empire of the Incas was the largest state-level society in the New World prior to the arrival of the Europeans. Their domain spanned over 4,000 km, including all of the highlands and coast of Peru, most of the highlands of Ecuador, northern Chile, part of western Bolivia, and part of north-western Argentina.

The Inca Empire was actually quite short-lived, lasting only about 100 years, from ca.1438AD, when the Inca ruler Pachacuti and his army began conquering the neighbours of the Inca heartland of Cuzco, until the coming of the Spaniards in 1532.

In Quechua, the language of the Incas, the empire was known as Tawantinsuyu, which means "land of the four quarters." As the name implies, the realm was divided into four parts, coming together at the capital of Cuzco: Chinchasuyu to the northwest, Condesuyu to the southwest,  Antisuyu to the northeast, and Collasuyu tothe southeast. Within the four quarters, the Incas ruled over people who had formerly composed hundreds of independent societies, representing dozens of different ethnic groups and perhaps as many different languages.

The Inca emperors were known by various titles, including"Sapa Inca," "Capac Apu," and "Intip Cori."Often, an emperor was simply referred to as the Inca. The traditional list of Inca rulers includes 11 emperors, in this order:

1      Manco Capac
2      Sinchi Roca
3      Lloque Yupanqui
4      Mayta Capac
5      Capac Yupanqui
6      Inca Roca
7      Yahuar Huacac
8      Viracocha Inca
9      Pachacuti Inca Yupanqui
10    Topa Inca Yupanqui
11    Huayna Capac

Manco Capac was the legendary founder of Cuzco, who began the Inca dynasty. There are several different Inca origin stories, which focus on Manco Capac and his brothers and sisters coming from the caves of Pacariqtambo or from Lake Titicaca to Cuzco. However, the Inca domain remained small, and for perhaps several centuries was no more significant in size or power than neighbouring societies in the Peruvian highlands. It was not until the ninth Inca, Pachacuti, that the Inca state began expanding and became a true imperial state. In fact, according to tradition, most of the land controlled by the Incas was conquered during the reigns of Pachacuti and his son, Topa Inca. A relatively small amount of territory was added by the eleventh Inca, Huayna Capac.

It is a matter of debate who should be accorded the status of the last independent Inca ruler: After Huayna Capac died in 1527, two of his sons, Huascar and Atahuallpa began a war for succession, each with their own claims to power.  Huascar had the support of much of the Inca nobility of Cuzco, while Atahuallpa was in charge of the army.  Atahuallpa actually had gained the upper hand by the time Francisco Pizarro arrived, and he probably would have assumed complete control over the empire and consolidated his power had it not been for the interference of the Spaniards.

The Incas controlled a vast territory that encompassed extremely rugged terrain and disparate climates, inhabited by perhaps over six million people. Those lands were home to people of dozens of different ethnic groups, representing numerous different languages.

The Incas used two main methods to subjugate the people of these lands. The first was military conquest, facilitated by their huge, well-equipped army. The second was diplomacy, in which the Incas offered the elites of the region the choice of submitting peacefully and gaining favour, backed by the threat of armed conquest.

To consolidate their control over the land and people of Tawantinsuyu, the Incas used various strategies of integrating the native political and religious systems into those of the empire. In many parts of the empire, they implemented a highly standardized administrative system based on units of ten (known as decimal administration).

The subjects of the Inca Empire were rigidly controlled, and were not allowed to travel freely. Instead of giving items in tribute, they were required to give a fixed amount of their labour to the state, which could have been dedicated to anything from building roads to making pottery.

The Incas are perhaps best known for their engineering works and architecture. They constructed an extensive system of well-built and constantly maintained roads, covering at least 23,000 km. The road network facilitated communications and the movement of people (especially the armies) and goods. To cross the many steep ravines found in the Andes, they built impressive suspension bridges. On the mountainsides in many regions, they built elaborate terraces to increase food production.

Inca architecture is well-known for its finely worked stones which, as the cliché goes, are fitted together so well, without the use of mortar, that you cannot fit a knife blade between the stones. As travellers to the Andes know well, that is indeed the case. In reality, the fine Inca stone work was reserved for the more important buildings erected by the state, and the Incas actually created more buildings of less exacting methods. The highest concentration of high quality Inca stonework is, of course, found in Cuzco and the surrounding region, in sites such as Machu Picchu and Ollantaytambo.

The Incas had no formal writing system, but relied instead on quipus, which were record-keeping devices based on a complicated system of knots. They had no wheeled vehicles, and transported all goods manually or with the use of llamas. The impressive engineering and architectural works were not produced using elaborate technology or secret techniques, but through the deployment of huge amounts of labour. Ultimately, the Inca achievement was the product of the highly developed organisational skills of the Inca elite, which enabled them to direct the people and resources of Tawantinsuyu.