These things take time. However since there was a war and the reasons for it were the king being selfish, as far as people know, the fact that the people of Grado would be real angry at their former king may speed up the process. I'd say that the first one to split up may have been between 15-20 years after the war, maybe less if things were left in a real turmoil back in Former Grado empire. The first one to split could have been...Irea? I don't know. 

Irea > Hiactance > Free City Taizel. The free city might have originally been part of Hiactance, but decided to become a state themselves.