[X] Let the Highlanders extract their vengeance and attempt to make amends after (-1 Legitimacy, -3 Diplomacy, possibility of war with Highlanders, chance of spawning new faction in the lowlands)
You guys advocating war will let the Thunder Horse win in the Lowlands and then proceed to become the Nomads part 2: from the east here to fuck You.
Also the damage from the Highlander war will lead to us getting damaged right before the Thunder a horse attack, that's if they don't decide to consolidate, which is worse if they have the Lowlands, as they will then outnumber us massively and we can't hit them before they do as we can't declare war without cause due to our traits.