A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
2 Kings (2 Samuel) 8:1
sa2 8:1DAVID SUBDUES THE PHILISTINES, AND MAKES THE MOABITES TRIBUTARY. (Sa2 8:1-2)
David took Metheg-ammah out of the hand of the Philistines--that is, Gath and her suburban towns (Ch1 18:1). That town had been "a bridle" by which the Philistines kept the people of Judah in check. David used it now as a barrier to repress that restless enemy.
2 Kings (2 Samuel) 8:2
sa2 8:2he smote Moab, and measured them with a line--This refers to a well-known practice of Eastern kings, to command their prisoners of war, particularly those who, notorious for the atrocity of their crimes or distinguished by the indomitable spirit of their resistance, had greatly incensed the victors, to lie down on the ground. Then a certain portion of them, which was determined by lot, but most commonly by a measuring-line, were put to death. Our version makes him put two-thirds to death, and spare one-third. The Septuagint and Vulgate make one-half. This war usage was not, perhaps, usually practised by the people of God; but Jewish writers assert that the cause of this particular severity against this people was their having massacred David's parents and family, whom he had, during his exile, committed to the king of Moab.
2 Kings (2 Samuel) 8:3
sa2 8:3HE SMITES HADADEZER AND THE SYRIANS. (Sa2 8:3-14)
Zobah-- (Ch1 18:3). This kingdom was bounded on the east by the Euphrates, and it extended westward from that river, perhaps as far north as Aleppo. It was long the chief among the petty kingdoms of Syria, and its king bore the hereditary title of "Hadadezer" or "Hadarezer" ("Hadad," that is, "helped").
as he went to recover his border at the river Euphrates--in accordance with the promises God made to Israel that He would give them all the country as far as the Euphrates (Gen 15:18; Num 24:17). In the first campaign David signally defeated Hadadezer. Besides a great number of foot prisoners, he took from him an immense amount of booty in chariots and horses. Reserving only a small number of the latter, he hamstrung the rest. The horses were thus mutilated because they were forbidden to the Hebrews, both in war and agriculture. So it was of no use to keep them. Besides, their neighbors placed much dependence on cavalry, but having, for want of a native breed, to procure them by purchase, the greatest damage that could be done to such enemies was to render their horses unserviceable in war. (See also Gen 46:6; Jos 11:6, Jos 11:9). A king of Damascene-Syria came to Hadadezer's succor; but David routed those auxiliary forces also, took possession of their country, put garrisons into their fortified towns, and made them tributary.
2 Kings (2 Samuel) 8:9
sa2 8:9Toi king of Hamath--CÅle-Syria; northwards, it extended to the city Hamath on the Orontes, which was the capital of the country. The Syrian prince, being delivered from the dread of a dangerous neighbor, sent his son with valuable presents to David to congratulate him on his victories, and solicit his alliance and protection.
2 Kings (2 Samuel) 8:10
sa2 8:10Joram--or Hadoram (Ch1 18:10).
2 Kings (2 Samuel) 8:11
sa2 8:11Which also king David did dedicate unto the Lord--Eastern princes have always been accustomed to hoard up vast quantities of gold. This is the first instance of a practice uniformly followed by David of reserving, after defraying expenses and bestowing suitable rewards upon his soldiers, the remainder of the spoil taken in war, to accumulate for the grand project of his life--the erection of a national temple at Jerusalem.
2 Kings (2 Samuel) 8:13
sa2 8:13David gat him a name when he returned from smiting of the Syrians--Instead of Syrians, the Septuagint version reads "Edomites," which is the true reading, as is evident from Sa2 8:14. This conquest, made by the army of David, was due to the skilful generalship and gallantry of Abishai and Joab. (Ch1 18:12; compare Psa 60:1, title.) The valley was the ravine of salt (the Ghor), adjoining the Salt Mountain, at the southwestern extremity of the Dead Sea, separating the ancient territories of Judah and Edom [ROBINSON].
2 Kings (2 Samuel) 8:15
sa2 8:15HIS REIGN. (Sa2 8:15-18)
David executed judgment and justice unto all his people--Though involved in foreign wars, he maintained an excellent system of government at home, the most eminent men of the age composing his cabinet of ministers.
2 Kings (2 Samuel) 8:16
sa2 8:16Joab . . . was over the host--by virtue of a special promise (Sa2 5:8).
recorder--historiographer or daily annalist, an office of great trust and importance in Eastern countries.
2 Kings (2 Samuel) 8:17
sa2 8:17Zadok . . . and Ahimelech . . . were the priests--On the massacre of the priests at Nob, [Sa1 22:19], Saul conferred the priesthood on Zadok, of the family of Eleazar (Ch1 6:50), while David acknowledged Ahimelech, of Ithamar's family, who fled to him. The two high priests exercised their office under the respective princes to whom they were attached. But, on David's obtaining the kingdom over all Israel, they both retained their dignity; Ahimelech officiating at Jerusalem, and Zadok at Gibeon (Ch1 16:39).
2 Kings (2 Samuel) 8:18
sa2 8:18Cherethites--that is, Philistines (Zep 2:5).
Pelethites--from Pelet (Ch1 12:3). They were the valiant men who, having accompanied David during his exile among the Philistines, were made his bodyguard.