Albert Barnes Commentary 1 Kings 15:6

"Now there was war between Rehoboam and Jeroboam all the days of his life." — 1 Kings 15:6 (ASV)

The writer repeats what he had said in 1 Kings 14:30 to remind the reader that Abijam inherited this war from his father.

The details of Abijam’s war are described in the marginal reference. That the author of Kings gives none of its details is consistent with his common practice in purely military matters. For instance, he gives no details of Shishak’s expedition and omits Zerah’s expedition altogether.