Why does it say "Gam Ashur"?
Rashi: Until now, they were careful to avoid foolish counsel; they did not join with evildoers. "Min ha'Aretz ha'Hi Yatza Ashur" (Bereishis 10:11) - they left the counsel of Dor ha'Flagah. Here, they joined and helped them for evil.
Rashi (based on Bereishis Rabah 37:4): Initially Ashur endeared good deeds; they separated from Nimrod - "Min ha'Aretz ha'Hi Yatza Ashur" (Bereishis 10:11). They returned to be Resha'im, and joined to destroy Your Bayis.
Radak: They were further from Eretz Yisrael than the other nations mentioned.
Radak citing his father: They continue to be evil; they do not remember their fall when Mal'ach Hashem struck their camp 1 .
Radak: According to this, this was after (Sancheriv's demise in the days of) Chizkiyah.
Why does it say "Hayu Zero'a li'Vnei Lot"?
Malbim: Amon and Mo'av were the primary fighters.
