One factor that contributed to the decline of both great zimbabwe and the mayans was

The empire became to large for the available resources. The people and the animals grew at an alarming rate. The capacity of the land area to supply crops, kindling, brushing and every single other need of life. Since the Great Zimbabwe individuals did not have the innovation to transport adequate supplies over long separations, the main option would have been to scatter the general population.

Corruption i think