Simplify the following text for a Grade 10 native English-speaking person.
Original: 1000 -- 1697 The Postclassic Era saw the collapse of many of the great nations and cities of the Classic Era , although some continued , such as in Oaxaca , Cholula , and the Maya of YucatÃ n , such as at Chichen Itza and Uxmal .
Simplified: Many of the great nations and cities of the Classic Era collapsed , but some continue , such as in Oaxaca , Cholula , and the Maya of YucatÃ n , such as at Chichen Itza and Uxmal .