Israel served not just one god, but gods.
In paganism, there were many gods, such as those of agriculture, business, love, music, and war. Each of these gods had their own area of influence. “Paganism therefore could accept the existence, but not the exclusive sovereignty, of the Lord. He could be one of many. He could even be first among equals. But he could not claim that he was the one true God; that his worshipers give him absolute lordship over every square inch of their lives; that ever to worship another god was spiritual prostitution.
"It was this belief system which had led to Israel’s failure to take all of Canaan; it was this belief system which the ongoing co-existence of the Canaanites encouraged and facilitated. The promised land was meant to be a place of worship of the Lord alone; it became the land of worship of the Lord plus.”1
12 And they abandoned the LORD, the God of their fathers, who had brought them out of the land of Egypt. They went after other gods, from among the gods of the peoples who were around them, and bowed down to them. And they provoked the LORD to anger.