The Maya civilization was interrupted by what many archeologists call "The Maya collapse", for some reason the Mayas abandoned their cities and lands and diminished greatly in numbers. When the Spanish "conquistadors" came, the Maya cities where abandoned, only a few people remained in the land but they weren't even a fraction of what the Mayas once where.

There are quite a number of theories that try to explain why this decadence occurred, here are some of the most important ones;

Earthquakes:

This appears to be one of the least likely to have occurred. Supposedly a massive earthquake could have swiped Maya land, killing thousands and destroying most of the cities.

It is based in the fact that most Maya cities are in ruins, and the high number of earthquakes that take place that occur in the highlands of Guatemala. However it's not very realistic because there are no earthquakes around the northern area (Yucatán), and the destruction of the cities could be a result of the intense growth of the wild life.

Epidemics:

This theory states that repeated breakouts of Paludism and yellow fever could have reduced the Mayas to a fraction of what they where forcing them to abandon their cities and homes in search of a healthier environment. However many scientists argue that these diseases didn't exist in America until the Spanish conquest.

Internal wars and conflicts:

It is know that there where many conflicts between the different Maya cities (Uxmal, Chiche Itza), it is possible that mayor wars between all the cites resulted in the destruction and economical looses of many cities forcing the Mayas to abandon them.


Invasions:

There are some people that suggest that foreign groups could have invaded and destroyed the Maya cities. However the idea of one external group destroying every city in the region is not very believable.