Would very much like to see the US do a firing squad of South Korean generals for refusing to get involved in a fight that would have glassed Seoul lol. Let’s be realistic and not write fanfic here.
You think America has all those troops in South Korea for just the brothels?
If and when the order comes, it won’t be delivered by just a runner. It’s going to be delivered by an America general that technically outranks all the non-Americans in the chain, and he won’t be walking into the command centre unarmed or alone.
The Americans are also not stupid and will not be issuing the attack order out of the blue as the very first order. It will be child’s play to start with something incontestable and relatively benign, like put all troops on alert, scramble alert fighters and prep the rest for immediate take off with full combat loads. Get the pieces in position and people moving and training and inertia will do the heavy lifting from there.
To refuse is to die, potentially right there on the spot. So unless you think the entire South Korea military is going to instantly mutiny wholesale as soon as actual combat orders are issued and get into firefights en mass with the Americans, there is little scope for them to be able to disobey or for individual disobedience to amount to much more than arrests or immediate public executions to prove a point and cow the rest.
This is the fucking military we are talking about. Not a country club. Direct orders from the correct chain of command that are legal per the standing rules cannot be questioned no matter how much you might want to or it doesn’t work at all.