Seren does not believe in the Lucellian faith, which earn the ire of the Church, so usually Vern would try to send an army every five years to try subjugating a part of Seren and propagate their faith.
Usually, in the past some High Lords in the Dukedom allowed the Vern troops to pass through their lands, while some in the South disagree with such acts.
The Northron lord likes the silver and gold they got from such transaction while the Southron lords did not like it because it would mean that they are opening themselves up for retaliation from Seren and also the detrimental effect of such act would do to their region security.
It is also the reason why the Southron lords and the Northron lords often butted head when The Noble Council is called and why they did not like each other that much
But now the Dukedom is united and it is clear to all that the young lord of Vermont would build a new Kingdom with King Adrian.