Why did God not drive Israel's enemies out of the Promised Land in one year?
The Lord withheld complete expulsion in a single year because Israel could not have kept pace with it. Rapid removal would leave the land desolate and cause wild beasts to multiply against them. Instead, He promised to drive the inhabitants out little by little until Israel increased and inherited the land.
Les explains that God told Israel He would destroy all the people they came to and make their enemies turn their backs and flee, but He would not drive them out in one year. The reason given is that sudden, complete removal would outpace Israel; they would not be able to keep up with it. The land would become desolate because they could not yet take care of it, and the beasts of the field would multiply against them. Therefore God would drive them out little by little until they increased and inherited the land. This connects to the promise given to Abraham that Israel's borders would extend from the River of Egypt and the Red Sea to the Euphrates River, and from the Judean desert to the Mediterranean, the whole Middle East promised to the nation of Israel.
I will not drive them out from before thee in one year; lest the land become desolate, and the beast of the field multiply against thee.