John Gill Commentary 2 Kings 3:7

"And he went and sent to Jehoshaphat the king of Judah, saying, The king of Moab hath rebelled against me: wilt thou go with me against Moab to battle? And he said, I will go up: I am as thou art, my people as thy people, my horses as thy horses." — 2 Kings 3:7 (ASV)

And he went and sent to Jehoshaphat the king of Judah, saying,
the king of Moab has rebelled against me
By refusing to pay him tribute:

wilt thou go up with me against Moab to battle? and he said, I will go
up ;
which he agreed to, partly to encourage in the reformation of religion which he had begun, and partly to chastise the Moabites for their invasion of his country, (2 Chronicles 20:1) .

I am as you are, my people as your people, and my horses as your horses ;
the same answer he returned to Ahab, (See Gill on 1 Kings 22:4).