In my 6th generation, I took a quick detour (less than 20 turns) to World 1, and upon my return to World 0, all of the buildings that I'd built (and reinforced with an iron hammer) were gone, the towns had become slums, and even the volcano (which was supposed to do Something Bad in a few more generations) was gone. 

None of the interesting or good things about this game are worth mentioning when your progress can be wiped out without any warning.