Heshbon was a major city located in Amon, which lay immediately north of Moab. This would be the most logical place to plan an invasion of Moab from the north. What is not clear is who the enemy is. The most likely invader would be the Babylonians, but the text is not specific. What is clear is the intention of the invader. Come let us cut her off from being a nation!
Total annihilation of Moab is the goal. Madmen
probably refers to another city in Moab. That too will be destroyed in the battle.
2 the renown of Moab is no more. In Heshbon they planned disaster against her: ‘Come, let us cut her off from being a nation!’ You also, O Madmen, shall be brought to silence; the sword shall pursue you.