Once God is done using Assyria to judge His own people, His wrath will be turned on them. Isaiah describes Assyria as a mighty forest.

"And the glory of his forest and his garden-ground will He destroy, even to soul and flesh, so that it is as when a sick man dieth.

The Assyrian army is compared to a "forest", for the number of men in it; and for the mighty men in it, comparable to large and tall trees, such as oaks and ...

The probable signification here, is that which refers it to a man wasting away with sickness, whose strength and vigor are gone, and who becomes weak and ...

18 The LORD will consume Assyria's glory like a fire consumes a forest in a fruitful land; it will waste away like sick people in a plague.

And it will be as when a sick man wastes away: Here the prophet speaks of a sick person gradually growing weak. The Hebrew word rendered wastes away (which can ...

(18) Both soul and body.--Literally, from the soul even to the flesh. The metaphor is for a moment dropped, and the reality is unveiled.

The glory of his forest and of his fruitful land the LORD will destroy, both soul and body, and it will be as when a sick man wastes away. Berean Standard Bible

David Guzik commentary on Isaiah 10 describes the judgment of God over Assyria inspire of the attack on Israel, who will have a remnant preserved.