Jamieson, Fausset and Brown on 2 Chronicles 36:21

21. until the land had enjoyed her sabbaths--The return of every seventh was to be held as a sabbatic year, a season of rest to all classes, even to the land itself, which was to be fallow. This divine institution, however, was neglected--how soon and how long, appears from the prophecy of Moses (see on Le 26:34), and of Jeremiah in this passage (see Jr 25:9-12), which told that for divine retribution it was now to remain desolate seventy years. As the Assyrian conquerors usually colonized their conquered provinces, so remarkable a deviation in Palestine from their customary policy must be ascribed to the overruling providence of God.

2Ch 36:22, 23. Cyrus' Proclamation.