I agree with what has been posted here, namely that Disney was drawing inspiration from collections of folktales that were in themselves dark and violent. Of course, the Brothers Grimm "lightened" them up a bit for popular, juvenile consumption. Originally folktales were the adult novels of the folk, and they were filled with violence. Disney's inspired adaptions of selected stories from the Grimm's collection were in keeping with the original published versions.
The links provided by /u/Searocksandtrees should be of use; if you have additional, subsequent questions, please ask.
Especially the trees. Not only in Snow White, but also in, for instance, the Disneyland 10th Anniversary documentary. Why?