What does "v'Nishbas Mivtzar" refer to?
Radak: It refers to Shomron, which was the stronghold of Efrayim and its capitol. "Mamlachah mi'Damesek" refers to killing Retzin Melech Ashur, and destroying Damesek.
Malbim: Via the fall of Damesek, the stronghold of Efrayim ceased; it was the fortress and protection of Efrayim.
Why does it say "u'She'ar Aram"?
Radak: Not only Damesek will be exiled; also the rest of Aram will be. Just like Kevod Bnei Yisrael, so they will be exiled. Melech Ashur exiled both of them at the same time.
What is the comparison to Kevod Bnei Yisrael?
Rashi: Just like the 10 tribes were [Malbim - already] exiled to Chalach and Chavor, Aram will be exiled to Kir - "va'Yagleha Kirah v'Es Retzin Hemis" (Melachim II, 16:9).
Radak: Refer to 17:3:2:1.
