What caused the fall of Israel

Around 20 years after Israel’s final fall, the nation of Judah, following repeated cycles of idolatry and reformation, was invaded by Assyria as well, reducing Judah "to a shadow of its former self, at least two thirds of the population perishing or being carried away captive" ("Judah," The Illustrated Bible Dictionary, 1980, Vol. 2, p. 825). Thus, a great number of Jews, Benjamites and Levites were also taken away to join the Israelite captivity.