For thousands of years, climate changes in the American Southwest dramatically affected the lives of the Anasazi people. Roughly 800 years ago, a series of droughts along with overpopulation gave way to starvation and warfare that shattered their civilization.
In 1090 and in 1130 acute droughts caused disaster to the Anasazi civilization in Chaco Canyon. The lack of rain, eroded and depleted soils, deforested mountains, and over-hunted wildlife, thus, starvation was widespread.
The Anasazi built small dams, dug irrigation ditches, and farmed on terraced slopes in order to capture water when the rains come. However, that method was pointeless and failed.
The Great House elite lost control of the citizens, and as a result they walked away from their pueblos toward the mesas and mountains of the north where more rain fell. By 1170, the Anasazi had left all their Great Houses.