Sacrifice of son.

Couldn't imagine the desperation Mesha (king of Moab) was in when he slain his firstborn (Moab's rightful heir) and offered him on the wall in the day of defeat against Jehoram, Jehoshaphat and king of Edom (in the days of Elisha). Not only was that his son, but his very firstborn, heir to Moab! What could have possibly induced this act unless the very kingdom of Moab is threatened to be taken? The whole nation had great indignation against Israel.