Charles Ellicott Commentary 1 Kings 14:21

"And Rehoboam the son of Solomon reigned in Judah. Rehoboam was forty and one years old when he began to reign, and he reigned seventeen years in Jerusalem, the city which Jehovah had chosen out of all the tribes of Israel, to put his name there: and his mother`s name was Naamah the Ammonitess." — 1 Kings 14:21 (ASV)

And Rehoboam. —Here begins the second series of the book—a series of brief annals, touching only the main points of the history of the kings of Israel and Judah, until the appearance of Elijah (1 Kings 17:1). Regarding the kingdom of Judah, and Israel insofar as it is connected with Judah, this account is largely supplemented by the fuller record of the Chronicles (2 Chronicles 11-17).

During this first period of the existence of the two kingdoms, lasting about sixty years, their relations appear to have been incessantly hostile, the aggression being on the side of the kingdom of Israel. In the reign of Rehoboam, the invasion by Shishak was probably instigated, perhaps even aided, by Jeroboam. Subsequently, the attack on Abijah, though victoriously repelled, seems a direct attempt at subjugation. Baasha pursues substantially the same policy, which is checked only by the desperate expedient of calling in the foreign power of Syria. Until at last, worn out by continual war against a superior force, Judah, even under such a king as Jehoshaphat, is forced to ally itself with the kingdom of Israel, apparently on a footing of something like dependence.