Isaiah 16:8
For the fields of Heshbon languish, and the vine of Sibmah: the lords of the heathen have broken down the principal plants thereof, they are come even unto Jazer, they wandered through the wilderness: her branches are stretched out, they are gone over the sea.
Isaiah 16:8 stands in the first division of Isaiah, chapters 1 to 39. That division is made up of single distinct prophecies given at different times and occasions during Isaiah's active public work as God's messenger to the rulers and the people, afterward gathered into one collection. Chapters 40 to 66 are unlike this, having been written in his later years apart from active work in the theocracy and being occupied wholly with the future. That future consolation is deliverance from the predicted Babylonian captivity by the God-sent monarch who would punish the oppressors and bring the people home, and deliverance from sin and error through the Messiah, sometimes interwoven and sometimes seen alone in the glory of God's spiritual kingdom and its exalted Founder.
Within that first division the verse is part of the predictions concerning Moab in Isaiah 13-16. It belongs to the prophecy against Moab. That prophecy addresses Moab as one of the oppressors of Judah.