1 Kings 16:21

Then were the people of Israel divided into two parts: half of the people followed Tibni the son of Ginath, to make him king; and half followed Omri.

Then were the people ... divided into two parts - i:e., the people principally, it may be presumed, of Tirzah, who supported Tibni, while Omri had the army on his side. The factions that ensued occasioned a four years' duration (cf. 1 Kings 16:15 with 1 Kings 16:23) of anarchy or civil war. Whatever might be the public opinion of Omri's merits, a large body of the people disapproved of the mode of his election, and declared for Tibni. The army, however, as usual in such circumstances (and they had the will of Providence favouring them), prevailed over all opposition, and Omri became undisputed possessor of the throne.