The ninth ruler of the Kingdom of Cusco, a gentleman by the name of Pachacuti, he decides to go on a fairly aggressive effort of expansion and it is Pachacuti that takes the Incas from the Kingdom of Cusco and creates an empire. Now as I mentioned, they did not call themselves the Incas. Inca was actually their word for ruler, so this was Pachacuti Inca. Their name for the empire that gets started by Pachacuti was Tawantinsuyu, and what it's really referring to is the four regions, and you can see the four regions here that were conquered with Cusco at the center. Now one of the interesting things is that right around the same time, we talk about it in another video, you have the Aztec Empire forming. The Aztec civilization exists well before that, as does the pre-Inca Empire civilizations, but in the 15th century is also when you have the Aztec Empire form. The Mayan civilization by this point is in its post-classical period.