Isaiah 9:19-21. “Through the wrath of the Lord of hosts is the land darkened, and the people shall be as the fuel of the fire: no man shall spare his brother. And he shall snatch on the right hand, and be hungry; and he shall eat on the left hand, and they shall not be satisfied: they shall eat every man the flesh of his own arm: Manasseh, Ephraim: and Ephraim, Manasseh: and they together shall be against Judah. For all this His anger is not turned away, but His hand is stretched out still.”
The word darkness here means turned into fuel for the fire. In verse 18 we read how the wickedness in the land will burn like a fire, consuming all in its path. Verse 19 tells us that even the people themselves will be fuel for that fire, committing terrible wickedness even in their suffering. Ephraim and Manasseh would turn against each other in civil war, and together they would turn against Judah. There would be cruelty, famine, and self-destruction. The Lord’s hand of judgment is still outstretched because the people will not forsake their sin.
You can read about all the circumstances and all that led up to these calamities in Nehemiah, chapter 9.