How did the Oompa Loompas come to live in Wonkas Factory ?

Oonpa Loonpas come from loompaland. Whole place is thick jungles, desolate wastes and the most horrid beasts in the world. They used to live in tree houses to escape the monsters, where they ate caterpillars, which, also according to Wonka, tasted revolting. He also saw that the Oompa-Loompas craved cocoa beans, so Wonka offered them to work and live in his chocolate factory, and they could have all the cocoa beans they wanted.