Dehumanization (or Deanimalization?)

In the beginning, the humans have been run out of the farm, already showing a decline in human (or animal) nature. Once the animals take over and resume the work of the humans, a steady decline is under way.

The "de-animalization" occurs weirdly-the pigs end up being the ones to become the most human. Apparently, the pigs are the most intelligent and in the end, become the most manipulative. Breaking the rules, modifying the 7 Commandments to accommodate to their wants, and lying to the other animals all result in the pigs becoming more treacherous than Mr. Jones.

They walk upon two legs, whip and abuse the animals, starve them, all while living in the luxury of the farmhouse, drinking, eating, and sleeping. Even a human, Mr. Frederick, tells Napoleon he treats the farm animals worse than his own!

Disaster

There weren't any major environmental disasters.

Destruction

There was a quite a bit of destruction in the novel. A windmill they attempt to build is destroyed twice (once allegedly by Snowball and another by humans). Also present is a metaphorical destruction. The original morals and ideals of Animal Farm crumble away and are "readjusted" by the pigs, as they slip into human nature.