Marry me, Your Highness | Yeonbin | forced marriage

Choi Yeonjun and Choi Soobin are both from different royale families who always rival each other. There was not a single day where they acted normally. Both of their sons are high-ranking princes of their family Kingdoms.
Choi Yeonjun - The Cheonsa's Kingdom
Choi Soobin The Pyeongjeong Kingdom
Both of these kingdoms are very powerful, but new ones appear over time until both kingdoms eventually become less influential than before. All that needs to be done is to somehow strengthen the government. At all costs. Both kingdoms are still very important in this world. No matter what. Their "sub-rulers" must continue to rule them.