See how the alliance began to work. Jehoshaphat is enticed into a battle. Ramoth-gilead in fact belonged to Jehoshaphat, for it was a city in the tribe of Gad. And yet Ahab it seems meant, had he conquered, to have united it to his kingdom.
Related Commentaries of 2 Chronicles 18:2
2 Chronicles 18:2-3
2 And aftera certain years he went down to Ahab to Samaria. And Ahab killed sheep and oxen for him in abundance, and for the people that he had with him, and persuaded him to go up with him to Ramothgilead.
3 And Ahab king of Israel said unto Jehoshaphat king of Judah, Wilt thou go with me to Ramothgilead? And he answered him, I am as thou art, and my people as thy people; and we will be with thee in the war.