the development of chronic warfare caused a breakdown in their fragile agriculture system. Imagine you were a farmer at the city-state of Uaxactun and you are at war with Tikal. Now, are you going to stay on your farm with no military protection? Of course not, you will move as fast as you can into the protection of the city walls. In the meantime your field becomes overgrown and no food can be produced. So we see cases of extreme food shortages that cannot be compensated for causing the demise of the Mayan culture.