Tractors? Why—no, there probably isn't a sensible reason. There rarely is in this sort of situation.

If you ever feel like depressing yourself with Previous history and some examples of how little human nature has changed, find some reading in the library on Mao Zedong and the Great Leap Forward, and then on the Khmer Rouge in Cambodia.

...on second thought, maybe you shouldn't. I mean, it's very interesting history, but it will make you feel grim about humanity for days.