2 Chronicles 11:1

Judah and Benjamin. The tribes of Judah and Benjamin now constituted the southern monarchy, which is usually called the nation of Judah. The tribe of Benjamin had formerly been more closely allied with the tribe of Ephraim, but it seems that the establishment of the capital at Jerusalem, on the border of Benjamin, was at least one factor influencing Benjamin to cast in its lot with Judah (see on 1 Kings 12:21).

Hundred and fourscore thousand. This is a moderate number, and probably represents the available trained men of war in the two southern tribes. At the time of the entrance into Canaan, Judah had 76,500 men, and Benjamin, 45,600 (Num. 26:22, 41), or a total of 122,100 males of military age. In David’s time Judah had 500,000 men (2 Sam. 24:9). The military forces of the kingdom of Judah as given in Chronicles numbered 400,000 at the time of Abijah (2 Chron. 13:3), 580,000 under Asa (ch. 14:8), and 1,160,000 under Jehoshaphat (ch. 17:14-18).