The Kids perceptions and mores change every generation (both in some multidimensional average and in their dispersion) based in response to their elder's beliefs and their material conditions. Those changes could be destructive or not, but the idea that "there is no truth" or we've reached "the end of history" mark a more dangerous part of the cycle.
But as Rome grew, wars tended to get farther and farther from home, so farmers could no longer tend to their farms, and also large influx of slaves made them noncompetitive against large slave-owners. So they had to sell their farms to those large owners, exacerbating the problem even more.
I honestly don't know any single revolution that happened for any reason other than inequality.