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. Its classical period is in bold right over here, but there are still many independent Mayan city-states in the Yucatan Peninsula, but the two notable empires here are the Aztecs and the Incas, which form in the 15th century. What makes them an empire is that you have one group, in the case of the Incas, the Kingdom of Cusco, conquering other peoples and taking tribute from them. Now what was interesting about the Incas is that they were able to form this large empire, the largest empire in the Americas at the time of the European conquest.