Mayan Collapse Theory

I think that the Mayan civilization collapsed because of several main reasons: One, Toltec invaders brought an unknown disease that the Mayans' immune systems never encountered; Two, overpopulation required more and more crops to be gathered, and the staple crop corn needed nutrients to survive, and those nutrients were not being replenished in the soil because the Mayans did not have crop rotation. Lack of nutrients provided for disaster, and I think a disease might have struck.
I think that yearly for the Maya, close to 785 AD, fewer and fewer crops were being harvested. The overpopulated and now hungry Copan region would have to wait for better years or start eating more of their other foods. However, the normal people remained weakened by hunger while the rich had enough to eat. Then, the region was invaded by the Toltecs. The Toltecs brought with them a disease which the Maya could not prepare for, having not had it previously. Thus, many of the Maya in this region died, but some escaped the disease because they were not fighting and were nowhere near the battles.