real politics is always played behind the screen

There was a rule regarding a 'key' battle or toppling another realm's Lord; everything was allowed.

There was no such thing as a dirty trick. You could use poison, seduction, conduct an assassination, stage a whole rebellion...anything was a fair game. 

This was why, as long as they could kill the Lord or snatch the Lord's key, there could not be any retaliation from the previous Lord. Of course, if someone else snatched the Lord's key in the next hour or even seconds, that would be fair game too. Thus, those who wanted to topple a Lord would make sure to plot carefully and prevent any faction from betraying them. 

But if you were to succeed? Whatever method you used, there wouldn't be any trial questioning the fairness of the method or the legitimation of the key holder. The residents of that realm just had to accept the change of the New Lord. 

That was, as long as you didn't fail and get caught.