Deuteronomy 29:25
Then men shall say, Because they have forsaken the covenant of the LORD God of their fathers, which he made with them when he brought them forth out of the land of Egypt: Then men shall say, Because they have forsaken the covenant of the LORD God of their fathers, which he made with them when he brought them forth out of the land of Egypt:
The calamities that came upon Israel happened because the people forsook the covenant of the Lord God of their fathers, which He had made with them when He brought them out of the land of Egypt. Forsaking that covenant meant turning aside to worship other gods. Because of that unfaithfulness, the curses of the covenant fell upon the land.