Deuteronomy 29:26
For they went and served other gods, and worshipped them, gods whom they knew not, and whom he had not given unto them: For they went and served other gods, and worshipped them, gods whom they knew not, and whom he had not given unto them:
Israel's calamity came because the people forsook the covenant they had made with God. They turned aside to serve and worship other gods, bowing down to deities they had not known. Those were gods God had not given to them and had no part in appointing for their worship. That idolatry provoked the Lord's anger against them and against their land. As a result the curses pronounced in the covenant fell upon the land in judgment.