Jamieson, Fausset and Brown on Hosea 6:11

11. an harvest--namely, of judgments (as in Jr 51:33; Joe 3:13; Re 14:15). Called a "harvest" because it is the fruit of the seed which Judah herself had sown (Ho 8:7; 10:12; Job 4:8; Pr 22:8). Judah, under Ahaz, lost a hundred twenty thousand "slain in one day (by Israel under Pekah), because they had forsaken the Lord God of their fathers."

when I returned the captivity of my people--when I, by Oded My prophet, caused two hundred thousand women, sons, and daughters, of Judah to be restored from captivity by Israel (2Ch 28:6-15). This prophecy was delivered under Pekah [Ludovicus De Dieu]. Maurer explains, When Israel shall have been exiled for its sins, and has been subsequently restored by Me, thou, Judah, also shalt be exiled for thine. But as Judah's punishment was not at the time when God restored Israel, Ludovicus De Dieu's explanation must be taken. Grotius translates, "When I shall have returned to make captive (that is, when I shall have again made captive) My people." The first captivity of Israel under Tiglath-pileser was followed by a second under Shalmaneser. Then came the siege of Jerusalem, and the capture of the fenced cities of Judah, by Sennacherib, the forerunner of other attacks, ending in Judah's captivity. But the Hebrew is elsewhere used of restoration, not renewed punishment (De 30:3; Psa 14:7).