Let alone Yan, even if the four eastern states united, it would be very difficult to completely exterminate the Barbarians.
This land is unsuitable for farming or immigration. Maintaining actual occupation of the desert is an unrealistic task.
If it were truly feasible, the Earl of North Border, having been established here for a century, would have done so long ago.
"This is something that can't be helped. You may not know this, but one hundred years ago, during the prime of the Barbarians' Golden Family, they placed enormous pressure on Yan.
One of my imperial ancestors, an Emperor, died in battle. The Crown Prince then immediately ascended the throne and personally led a campaign.
Now that we've finally managed to subdue the Barbarians, we naturally cannot give them the opportunity to rise again."
"Your Highness, you've misunderstood my meaning."
"Fine, you're full of witty remarks. Continue."