1 Kings 11:21

when Hadad heard in Egypt that David slept with his fathers Hadad's first attempt to depart from Egypt was therefore soon after Solomon's accession. It is clear however from the history that it was only after some pressure that the Egyptian king allowed him to go. The mischief that he did (see 1 Kings 11:25) would be by stirring up his countrymen to cast off the yoke of the Israelites. We must allow a considerable time for any revolt to be organized, and we are not told that any outbreak really took place, but only that mischief was done through Hadad's agitation.

and that Joab the captain of the host was dead Joab's name would be one to spread terror, because of the severity he had displayed toward Edom. (See above, 1 Kings 11:15-16.) Hadad therefore waited to hear of his death also, before he ventured to take any step for his own restoration.