The Incas were an ancient people who lived in South America. Their unique culture began to spread during the 12th century, and within 400 years they controlled a larger territory than any other South American cultural group had ever controlled. At its largest, over one million Incas lived in a territory hugging the western coastline of South America from Ecuador in the north to what is now Chile in the south.

The Inca culture spread by conquering other cultural groups. Installing local leaders into the Incan government, they were generally generous toward anyone who defended the Incan culture against intruders. They also made a point of providing favorable treatment to all people who did not resist conquest.

The leader of the core group of Incas was called the Inca and was considered to be a divine descendant of the sun god — the most important god of their polytheistic religion. The Inca had absolute power, and immediately below him in the social hierarchy was his royal family. The royal family was made up of the Inca's siblings, parents, wife, children, and concubines. Below the royal family were the tribal heads, who each led a clan. Below the tribal heads were the commoners, who were organized in groups of tens, with a boss for each group. This strict hierarchy strongly discouraged individual social advancement and created a highly centralized society.

The Incas managed some impressive feats, such as large-scale terracing of mountainsides and building many stone structures without the help of mortar. They were so successful at terracing that during the heyday of the Incas, there was more cultivated land in the Andean highlands than there is in modern times. Perhaps their most well-known terraced mountain-ridge is Machu Picchu in Peru — a symbol commonly associated with the Incas.

The Incas also built many large buildings with stones that were so precisely cut that they did not require mortar. Because of their building prowess, many of their buildings are still standing today. They also used their stone-cutting skills to build roads complete with tunnels and bridges throughout the Andes, and they built aqueducts to bring water to their cities.

Their language is called Quechua, which is still spoken by many indigenous peoples living in the Andes. Instead of writing, the Incas used colored knotted cords called quipu to keep records. They were also highly accomplished in mathematics, medicine, and astronomy.

In 1531, Spaniard Francisco Pizarro invaded the Incas. With only 200 soldiers he managed to kidnap Atahualpa, the then-current Inca. Atahualpa resisted Pizarro's attempts to use him as a puppet ruler, so Pizarro executed him in 1533. After another forty years of struggles, the Spanish finished conquering the Incas in the 1570s.