1)
What is the meaning of "Hiv'ish b'Amo"?
1.
Radak: He fights them, and will not make peace with them. He despises them, like one despises something Niv'ash (spoiled).
2)
Why does it say "b'Amo v'Yisrael"?
1.
Malbim: It was feasible that David fights with Yisrael, and Yehudah, David's Shevet, supports him. Or he fights with his Shevet, to find grace in the eyes of Yisrael, lest they say that he leans to favor his Shevet. Since he fights also with Yehudah and Keini, who are from Yisrael, he despises all of them.
