I think it is rather about 'mounting the tiger'.
The aying that once you ride the tiger you cannot get off and have to wait were it stops.
Once you declared for one king, you must either make sure he wins or he dies.
Both of these are hard, not to mention the myriad of difficulties to this, like loyalty, hate, antipathy, duty, oathes, etc. but thats the beginning and the end of it: If you want your skin intact you need to be on the winning side or at least at the winnings side good side.
(Also Bolton himself might be reasonable sane, but his son most definitly is not, which is a strike against Bolton and as well as the fact that Bolton is a traitor, which bodes ill for his trustworthiness and thats what feudal relationships are based on).
So once you commited you need to facilitate a favourable outcome.
You cannot just stop, unless your whole group stops because then you will be torn apart (nobody likes a traitor). Or you can, should you feel you picked the wrong side, try to ingratiate yourself with the either side, but that is dangerous business because nobody likes a traitor.
That is why after a rebellion usually blanket pardons are given: It is the only way to make sure business as usual can start again.
But Stannis' folks know that he will not falter. He had his last hand burned (for a certain measure of accurateness at least) because he tried to make peace, calling it treason.
And Roose Bolton and especially Ramsay has also established a reputation that means you do not want to surrender to him.
So everybody in the North is caught between the rock and the hard place. Both sides DEMAND your fealty, neither wants to pay and both sides are most likely to cull the unaligned first, so you pick a side just to be out of most obvious spot of danger, which leaves you all other matters of trouble.
Bolton might have you skinned for all you know and Stannis caught off the upper fingers of the man who saved his hide, so mercy is in extremly short supply and 'uniting' is unlikely because neither is so fearsome that you would just risk what they might do to you if you surrender to avoid what they will do to you when, not if, they get hold of you.
Same in the south, look what happened when certain lords decided they did not like what Catelyn did with Jaime and Robb reacted.
You cannot just go your way and quit the game because if your king lets you do that he risks his whole army.
So peace needs to come from the top or from the middle-level in one huge, all encompassing sweep (we are talking severe disaffection with 80-90% of the lords) and needs to made with the other sides top tier.
'Imagine there is a war and nobody comes' is not an option in Westeros anymore.
Which means you need either all but one pretender(-party) dead or have one side so obviously and certainly outnumbered, demoralised and broken that they break apart almost by themselves, the capitulation little more than a formality. Neither side has reached either point so far.
Stannis troops are still quite disciplined and moral remains high because he is the messiah (kinda) and the Boltons power in the North as the Freys in the Riverlands is not all it should be (since both have proven themselves untrustworthy and unreliable, poison to a liege-vassal-ralationship) living wriggle room.
So, to sum it:
You need for a peace
- a winning side know for mercy and fairness or on just having issued a general pardon (how Robert pacified the realm)
- a winning side so powerful that everybody knows even a show of resistance might any squash any hope of mercy though there still needs to be a chance for mercy, because if you KNOW you and your whole household gets skinned, well you might as well fight as long as you can.
and you need a losing side that has
- just lost its leader so the mid-level managment can just wander off and get themselves a new alligance with a minimum amount of fuss and internal strive (though i think there might have been some purging even when the Roses changed sides)
- is so demoralised, broken and beaten that all you need to do is finishing them off, which would not make you break a sweat, and any reasonable man knows it. In that case either a consensus of the sensible gets established, probably with an 'unfortunate accident' happening to the faction leader and the whole faction throw itself at the mer of the winner or everyone but the hard core gets killed off in a coup d'etat and you only need to mop them up with most running as soon as the iron hand that holds them together disappears.