The Lord made a covenant with Israel, but He also worked with the rest of the world, and if they went totally into sin, He dealt with them accordingly. In the case of the Canaanites, the Lord used Israel to destroy the Canaanites, because their corruption had grown so badly that He had to remove them from the land and give Israel the Land of Canaan,

Thus Joshua took all this land: the mountain country, all the South, all the land of Goshen, the lowland, and the Jordan plain—the mountains of Israel and its lowlands, from Mount Halak and the ascent to Seir, even as far as Baal Gad in the Valley of Lebanon below Mount Hermon. He captured all their kings, and struck them down and killed them. Joshua made war a long time with all those kings. There was not a city that made peace with the children of Israel, except the Hivites, the inhabitants of Gibeon. All the others they took in battle. For it was of the Lord to harden their hearts, that they should come against Israel in battle, that He might utterly destroy them, and that they might receive no mercy, but that He might destroy them, as the Lord had commanded Moses (Joshua 11.16–20).

The Canaanites had their chance, but they wasted it and so the Lord removed them by the hand of Israel with no mercy. All of those peoples have disappeared off the face of the Earth.

The Lord still operates this way, but Christians and the church can be of help by being the salt of the Earth and the light of the world, that people might turn to the Lord and clean up their lives, and thus live!