Moab was being judged for the sin of burning the bones of the king of Edom to lime. Thus, they were not being punished for anything that they did to Israel or Judah, but for the way in which they treated another heathen king. This implies that God’s judgment was based on a universal ethic of divine justice which was obvious to all people.
1 Thus says the LORD: “For three transgressions of Moab, and for four, I will not revoke the punishment, because he burned to lime the bones of the king of Edom.