Which kings are discussed here?
Malbim: It is the kings of the south.
What do we learn from "Pa'am Achas"?
Radak: He did not need to besiege cities. The war did not stretch out. He conquered all of them at once, one after one, without interruption.
Malbim: These he conquered at once, but kings in the other parts of the land, he did not conquer them at once, like it says in the coming Perek.