Saul having thus been cut off, David, when the news of his death was brought to him in the land of the Philistines, is related to have wept, and to have given a marvelous proof of his affection. He then betook himself to Hebron, a town of Judæa; and, being there again anointed with the royal oil, received the title of king. But Abenner, who had been master of the host of King Saul, despised David, and made Isbaal king, the son of King Saul. Various battles then took place between the generals of the kings.
Abenner was generally routed; yet in his flight he cut off the brother of Joab, who had the command of the army on the side of David. Joab, on account of the sorrow he felt for this, afterwards, when Abenner had surrendered to King David, ordered him to be murdered, not without regret on the part of the king, whose honor he had thus tarnished. At the same time, almost all the older men of the Hebrews conferred on him by public consent the sovereignty of the whole nation; for during seven years he had reigned only in Hebron.
Thus, he was anointed king for the third time, being about thirty years of age. He repulsed in successful battles the Philistines making inroads upon his kingdom. And at that time, he transferred to Zion the ark of God, which, as I have said above, was in the town of Cariathiarim. And when he had formed the intention of building a temple to God, the divine answer was given him to the effect, that that was reserved for his son. He then conquered the Philistines in war, subjugated the Moabites, and subdued Syria, imposing tribute upon it.
He brought back with him an enormous amount of booty in gold and brass. Next, a war arose against the Ammonites on account of the injury which had been done by their king, Annon. And when the Syrians again rebelled, having formed a confederacy for war with the Ammonites, David entrusted the chief command of the war to Joab, the master of his host, and he himself remained in Jerusalem far from the scene of strife.
Source: Sacred History (New Advent)