Zerah the Ethiopian - Probably of that Ethiopia which lay on the south of Egypt, near to Libya, and therefore the Libyans are joined with them, 2 Chronicles 16:8.
A thousand thousand - If this people had come from any great distance, they could not have had forage for such an immense army.
Zerah the Ethiopian is probably Usarken (Osorkon) II, the third king of Egypt after Shishak, according to the Egyptian monuments. Osorkon II may have been by birth an Ethiopian, for he was the son-in-law, not the son, of the preceding monarch, and reigned in right of his wife. The object of the expedition would be to bring Judaea once more under the Egyptian yoke.
An host of a thousand thousand - This is the largest collected army of which we hear in Scripture; but it does not exceed the known numbers of other Oriental armies in ancient times. Darius Codomannus brought into the field at Arbela a force of 1,040,000; Xerxes crossed into Greece with certainly above a million of combatants.