What are "Netzivim"?
'Rashi': They are governors. He did not want to put a king [who would be submissive to David].
Rashi (Shmuel II, 8:14): They are appointees to collect taxes.
It says above (verse 6) that Hashem saved David. Why is this repeated?
Malbim (Shmuel II, 8:14): David conquered Aram Naharayim (Surya) against the Halachah (Sifri Sof Ekev. We must conquer all of Eretz Yisrael before going to conquer out of Eretz Yisrael! This is called Kivush Yachid, like the Rambam says.) Even so, Hashem saved him. He foreshadowed the future, when He will add to Eretz Yisrael the lands of Kini, Kenizi and Kadmoni, i.e. Edom, Amon and Mo'av.
Rashi in Shmuel writes that the Netzivim were appointees to collect taxes. It says in Melachim I, 11:15 that Yo'av killed all the males!
Malbim (Melachim I, 11:15): Initially, David put Netzivim. Later, Edom rebelled, and they killed all the males 1 .
Perhaps they collected taxes from the females, or from other nations who came to live there after he killed all men of Edom. (PF)
Malbim (Shmuel II, 8:13) said that after Edom rebelled, David put Netzivim in all of Edom! (PF)
