Many of the great nations and cities of the Classic Era collapsed, but some continue, such as in Oaxaca, Cholula, and the Maya of Yucatán, such as at Chichen Itza and Uxmal. This is sometimes seen as a period of increased chaos and warfare. The Toltec for a time dominate central Mexico in the 11th - 13th century, then collapse. The northern Maya are for a time united under Mayapan. The Aztec Empire rises in the early 15th century and seems on the path to gain a dominance over the whole region not seen since Teotihuacan, when Mesoamerica is discovered by Spain and conquered by the Conquistadores.