Jamieson, Fausset and Brown on Leviticus 26:34

34. Then shall the land enjoy her sabbaths, as long as it lieth desolate, &c.--A long arrear of sabbatic years had accumulated through the avarice and apostasy of the Israelites, who had deprived their land of its appointed season of rest. The number of those sabbatic years seems to have been seventy, as determined by the duration of the captivity. This early prediction is very remarkable, considering that the usual policy of the Assyrian conquerors was to send colonies to cultivate and inhabit their newly acquired provinces.