Not only that but there is a limit to how much distance the dragons can go out from the hiryuu castle without losing their powers, if Su-won were to continue his expansion, Yona and co could sabotage him from inside the kingdom, but they could never come to aid efficiently outside of the Kouka borders, with the exception of Hak and possibly Zeno, depending on how much distance he can go before his powers start working, he did say his regen was staggered due to the distance, if Kouka citizens or troops outside of the borders are located, it could end very badly for Su-won, since he always had at least a degree of support from them in his militar affairs, even if he´s a genius, there´s a chance he will lose battles as well, if he´s pitted against other genius military generals.
They agree with him, mostly on a nationalism POV, plus the neighbour countries, got the rep. of slaver vandals (in Awa) and terrorist merchants (with Nadai selling traffic), tried and suceeded corrupting one allied tribe into a coup, that would´ve killed thousands and humiliated the Fire tribe´s pride, I can see how such deeds can create a very huge grudge and huge desire for payback, but it remains to be seen, if su-won will bring a more dark justice to his deeds, or if he will keep it controlled like he has done so far, if he wages war with the South Kai, he will need to do very dirty things to win his fights, but right now he´s building up his power in Kouka.
