What is the meaning of "v'Yismarmar"?
Ibn Ezra: This is like "Simi Lach Tamrurim 1 " (Yirmeyah 31:20).
Metzudas David: He was cruel with great bitterness.
Malbim: Normally, Melech ha'Negev indulged in pleasures. When he saw Melech ha'Tzafon enter his border, he became bitter.
The Meforshim there explain, make markers so you will know how to return; surely you will succeed and return. (PF)
Why does it say "v'Nilcham Imo Im Melech ha'Tzafon"?
Ibn Ezra: Sometimes a verse uses a pronoun (the suffix Vov in Imo) and later explains it, e.g. "va'Tir'ehu Es ha'Yeled."
Who amassed a multitude?
Ibn Ezra, Malbim: Melech ha'Negev.
What multitude was defeated?
Rashi: That of Melech ha'Tzafon.
