Adam Clarke on 2 Kings 14:8

Come, let us look one another in the face - This was a real declaration of war; and the ground of it is most evident from this circumstance: that the one hundred thousand men of Israel that had been dismissed, though they had the stipulated money, taking the advantage of Amaziah's absence, fell upon the cities of Judah, from Samaria to Beth-horon, and smote three thousand men, and took much spoil, 2Chr 25:10-13. Amaziah no doubt remonstrated with Jehoash, but to no purpose; and therefore he declared war against him.