The glory days were not to last very long, and by 750 AD political and social changes began to be felt: alliances and trade links broke down, warring increased and stelae were carved less frequently. Cities gradually became depopulated and new construction ceased in present-day Guatemala after about 830 AD. It is uncertain what factors precipitated the downfall of the Maya: an increase in population probably put great strains on food production, perhaps exhausting the fertility of the soil, while climate changes could also have been influential; there may also have been peasant revolts against the ruling elite. By the tenth century, the Maya had abandoned their cities in Petén and those few Maya that remained were reduced to a fairly primitive state.

By the Postclassic period (900 AD to the Spanish Conquest) all the city states in Guatemala had collapsed. The decline of Maya civilization in the heartland of Petén brought about a rapid depopulation which prompted an influx of people into the Guatemalan highlands to the south. Along with the Yucatán, this area, formerly a peripheral region of relatively little development, now contained the last vestiges of Maya culture. Small settlements remained scattered throughout the highlands, usually built on open valley floors and supporting large populations with the use of terraced farming and irrigation. Little was to change in this basic village structure for several hundred years.