...that makes no sense to me tbh b/c remember in the beginning of the chapter, the King told Yona she could marry anyone else besides Soo-Woon, it would mean that the King likely knows what Soo-Woon is plotting, but then again, who knows right? ╮(￣▽￣)╭
I think it was anyone but Soo-Won because of all that mysterious antagonism between King Il and Soo-Won's father. Wasn't Soo-Won's father the rightful heir to the throne? Wasn't he secretly killed by Il at some point after Il became king? Think there was some 'bad blood' there.
I don't think King Il would have to go that far. If he finally recognized that his pacifistic policies were destroying the kingdom, all he had to do was change his policies. All four tribes would have been behind him instantly.
And as far as Yona's safety, far safer to get Yona married or have a steward in place to assist her and 'get sick' or 'have an accident' than set up a coup with someone you don't even respect enough to let your daughter marry. Coups are messy and you have no control over the end result.
What if the King asked Woon to kill him?
He coul have done that to protect the kingdom couldn't he?