Malbim: This refers to verse 11, which said that the agitator of kingdoms, his hand is stretched to the sea. Who is this? It is Eretz Kasdim.

Rashi: It was not worthy to be a nation. They are called "ha'Goy ha'Mar veha'Nimhar" (Chabakuk 1:6). It is a foolish nation - one of three ¹ that Hashem regrets creating them (Sukah 52b).

Radak #1: Bavel, Ninveh and the rest of the land called Bavel nowadays, was not earlier.

Radak #2: This refers to Tzor. This city was of Kasdim. They (Anshei Tzor) did not build it, rather, Ashur founded it for their ships.

Radak #3: Eretz Kasdim is greater than you (Tzor), and the Creator will destroy it via Paras and Madai, to the point that those who see it will say 'this nation was not.'

Malbim: It was not important at all in olden days.

Rashi: They are big boats, like "Tzi Adir" (33:21). Ashur put its boats to remain there.

Radak #1: They are those who dwell in a Midbar Tziyah (dry). This is like "Lefanav Yichre'u Tziyim", "l'Am l'Tziyim" (Tehilim 72:9, 74:14). Ashur established Bavel, so people who used to dwell in tents in dry Midbaros would live there. "Min ha'Aretz ha'Hi Yatza Ashur va'Yiven Es Ninveh v'Es Rechovos Ir v'Es Kalach" (Bereishis 10:11). Kasdim are Bnei Kesed ben Nachor. They conquered this land, and nowadays it is called Eretz Kasdim. Ashur founded it earlier, therefore it is included in Ashur, and those who rule over it are called kings of Ashur. However, today it is of Bavel and the Kasdim, for they conquered it.

Radak #2: They are dry deserts Similarly, Hashem will destroy Ashur, and He will found Ashur for dry deserts and wild animals. They set up towers, and He made it for ruins!

Malbim: They are boats. Bavel was in the waste-heap, and Ashur lifted them, and taught them to go in boats.

Radak: You should not be astounded to hear that Tzor will be destroyed. Also the army of Kasdim, which comes to destroy them, used to belong to another, and they took it from the first ones, and later, others will take it from them. This is the way of the world - this one rises, and this one descends. This teaches that Kel is Master over the entire land.

Malbim: This shows the might of Ashur. Via the boats that Ashur founded for Bavel, they will destroy the castles of Tzor.

Rashi: They will erect their fortresses on Tzor. Vachunav is an expression of "Ofel va'Vachan" (32:14), i.e. towers that they make to besiege cities.

Radak: They erected the fortresses now in Bavel, and "destroyed the [previous] castles."

Malbim: This was a test to show the might of Ashur. Refer to 23:13:4:2.

Rashi: They will destroy. This is like "Aru Aru" (Tehilim 137:7), demolishing until the foundation.

Radak: It is breaking, like "Ar'er Tis'ar'ar" (Yirmeyah 51:58).

Radak: It refers to the king. All Goyim are included.

Malbim: It means that Bavel will make Tzor [a ruin].