The Tzeltal are one of the descendants of the Maya, which was one of the early and largest Mesoamerican cultures. This group left behind a large number of archeological sites such as Tikal and Palenque, and the Mayan linguistic group is one of the largest linguistic groups in the Americas, subdivided into Huastec, Yucatec, eastern Maya and Western Maya. Mayan civilization reached its height in the Classic period of Mesoamerican chronology, but from 900 to 1200 CE went through a period of decline into smaller, rival city-states with almost all cities completely abandoned by the 15th century. It is not known to Western scholarship why Mayan civilization collapsed. From this point on, various Mayan-dialect speaking peoples formed related but distinct cultures with various related languages. The Spanish conquered Mayan territory in the early to mid 16th century including what is now the state of Chiapas. Over most of the colonial period until the Mexican Revolution, this and other indigenous groups were forced to labor in the mines, mills and haciendas of the state for little to no wages. Even during the 20th century economic and political marginalization remained severe, culminating in the Zapatista uprising in 1994, in which many of the Tzeltal people participated along with other indigenous groups.