Its almost like he realized that he spent TOO LONG on the pre-state conquering segment of the manga... that when we actually started getting into the REAL UNIFICATION part, he had to speed up it up, or else he ends up writing another 800+ chapters...
Let me rephrase this: we spent over 800 chapters and yet not a single state has been defeated yet.
Not every mangaka is a crackhead like Loda who is content spending half his lifespan writing the same trash over and over. Hara is around his age, but did not receive the same popularity, advertising and opportunities as the OP franchise did.
Kingdom started in 2006 and has been running for almost TWO DECADES by now. You can already see the cracks appear in the writing and the art. Just compare recent arcs like Hango or Gian to old ones like Bayou and Sanyou and the difference is honestly like night and day.
Its sad to see, but it looks like we'll be slugging through horribly put-together arcs from now on, where there is no more passion put into the writing, so we get lame random melee duels here and there with no clever thought behind them, until Hara can fill his checklist of "yep, this state is done, now next one..."

