Charles Ellicott Commentary 1 Kings 15:21

"And it came to pass, when Baasha heard thereof, that he left off building Ramah, and dwelt in Tirzah." — 1 Kings 15:21 (ASV)

Dwelt in Tirzah —that is, returned to his own capital: in the first instance, of course, retiring to meet the new enemy in the north, and then obliged to give up his attempt against Asa. From 1 Kings 20:34, it seems as if, until the time of Ahab, Syria retained its conquests and a certain supremacy over Israel. Baasha may have had to buy peace by undertaking to leave Judah unmolested, which might be considered a tributary of Syria.