Albert Barnes Commentary 1 Kings 1:35

"Then ye shall come up after him, and he shall come and sit upon my throne; for he shall be king in my stead; and I have appointed him to be prince over Israel and over Judah." — 1 Kings 1:35 (ASV)

Over Israel and over Judah - There is no anticipation here of the subsequent division of the kingdom; the antithesis between Judah and Israel already existed in the reign of David (2 Samuel 2:9; 2 Samuel 19:11).