I enjoyed the book--not quiet as much as everyone else though... =/
In the final chapter, drastic change took place. One of the main reasons for such change can be symbolic to the heavy rain fall that occurred in Macondo. The rain that lasted many years in Macondo is similar to the flood of 40 days in the Bible. The flood in the Bible washed out humanity, except for the selected few that were considered worthy to live; the flood cleaned to earth of the dirt and filth; and the flood gave life back to the earth after it ended, but with better hopes of surviving. Like the flood, Macondo's rain is meant to clean the city of the unworthy and conspicuous families, the dirt and scum that infested the lives of everyone, and after the rain, only the strongest and worthy would be able to enjoy the new land.
Also like the Bible, where the downfall began with Adam and Eve, I ultimately believe that the destruction of the town was due to the first incest relationship (Jose and Ursula). Their relationship lead to the destructions of all the other relationships, people, and finally, the city of Macondo.