Exodus 23:28-30

I will throw your enemies into panic; I will drive out the Hivites, the Canaanites, and the Hittites as you advance. I will not drive them out within a year's time; if I did, the land would become deserted, and the wild animals would be too many for you. Instead, I will drive them out little by little, until there are enough of you to take possession of the land.