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
1 Chronicles 19:1
ch1 19:1DAVID'S MESSENGERS, SENT TO COMFORT HANUN, ARE DISGRACEFULLY TREATED. (Ch1 19:1-5)
after this--This phrase seems to indicate that the incident now to be related took place immediately, or soon after the wars described in the preceding chapter. But the chronological order is loosely observed, and the only just inference that can be drawn from the use of this phrase is, that some farther account is to be given of the wars against the Syrians.
Nahash the king of the children of Ammon died--There had subsisted a very friendly relation between David and him, begun during the exile of the former, and cemented, doubtless, by their common hostility to Saul.
1 Chronicles 19:3
ch1 19:3are not his servants come unto thee for to search?--that is, thy capital, Rabbah (Sa2 10:3).
1 Chronicles 19:4
ch1 19:4shaved them--not completely, but only the half of their face. This disrespect to the beard, and indecent exposure of their persons by their clothes being cut off from the girdle downwards, was the grossest indignity to which Jews, in common with all Orientals, could be subjected. No wonder that the men were ashamed to appear in public--that the king recommended them to remain in seclusion on the border till the mark of their disgrace had disappeared--and then they might, with propriety, return to the court.
1 Chronicles 19:6
ch1 19:6JOAB AND ABISHAI OVERCOME THE AMMONITES. (Ch1 19:6-15)
when the children of Ammon saw that they had made themselves odious to David--One universal feeling of indignation was roused throughout Israel, and all classes supported the king in his determination to avenge this unprovoked insult on the Hebrew nation.
Hanun . . . sent a thousand talents of silver--a sum equal to Â£342,100, to procure the services of foreign mercenaries.
chariots and horsemen out of Mesopotamia . . . Syria-maachah, and . . . Zobah--The Mesopotamian troops did not arrive during this campaign (Ch1 19:16). Syria-maachah lay on the north of the possessions of the trans-jordanic Israelites, near Gilead.
Zobah--(see on Ch1 18:3).
1 Chronicles 19:7
ch1 19:7So they hired thirty and two thousand chariots--Hebrew, "riders," or "cavalry," accustomed to fight either on horseback or in chariots, and occasionally on foot. Accepting this as the true rendering, the number of hired auxiliaries mentioned in this passage agrees exactly with the statement in Sa2 10:6 : twenty thousand (from Syria), twelve thousand (from Tob), equal to thirty-two thousand, and one thousand with the king of Maachah.
1 Chronicles 19:8
ch1 19:8David . . . sent Joab, and all the host of the mighty men--All the forces of Israel, including the great military orders, were engaged in this war.
1 Chronicles 19:9
ch1 19:9children of Ammon . . . put the battle in array before the gate of the city--that is, outside the walls of Medeba, a frontier town on the Arnon.
the kings that were come were by themselves in the field--The Israelitish army being thus beset by the Ammonites in front, and by the Syrian auxiliaries behind, Joab resolved to attack the latter (the more numerous and formidable host), while he directed his brother Abishai, with a suitable detachment, to attack the Ammonites. Joab's address before the engagement displays the faith and piety that became a commander of the Hebrew people. The mercenaries being defeated, the courage of the Ammonites failed; so that, taking flight, they entrenched themselves within the fortified walls.
1 Chronicles 19:16
ch1 19:16SHOPHACH SLAIN BY DAVID. (Ch1 19:16-19)
And when the Syrians saw that they were put to the worse before Israel--(See on Sa2 10:15-19).
1 Chronicles 19:18
ch1 19:18David slew of the Syrians seven thousand men--(Compare Sa2 10:18, which has seven hundred chariots). Either the text in one of the books is corrupt [KEIL, DAVIDSON], or the accounts must be combined, giving this result--seven thousand horsemen, seven thousand chariots, and forty thousand footmen [KENNICOTT, HOUBIGANT, CALMET].