Mongol invasion of Japan: What does it take?

I am in the works of trying to make a post-Genpei War timeline that sees Japan stay unified (no Sengoku period). The main PoD being a successful Mongol invasion that turns Japan into a client state, and thus weakens the Daimyos.

However, both invasions were tremendous failures, the first barely even approaching Japan at all.

What would it take for the Mongols to, at the very least, force peace terms upon Japan? What needs to be handwaved, or does it stray too far into impossibility?
 
Kublai needs to actually make a proper fleet instead of rushing Japan with riverboats, for one. He needed at least five years to make a fleet worthy of taking on Japan. The one he used was constructed and seized over a single year.

That said, Mongols taking over Honshu is improbable. Maybe Kyushu, but beyond that it's unlikely they can push and hold land much further. The Japanese might not have seen war in a very long time prior to the first invasion but Japan's mountains and forests make an invasion rather difficult and it being an archipelago makes suppressing revolts rather difficult (especially for a nation without naval tradition).

Also, probably want to not have the Yuan bleed out in Vietnam since that was a horrific waste of money and lives, aside from breaking the perception of Mongol invincibility.

So I'd say, to start at least, have Kublai be a bit more patient (have the Goryeo be a bit less eager for war, perhaps? The Goryeo king offering whole-hearted support and the Goryeo navy didn't help matters) and construct a seaworthy fleet (so that, even if they face opposition, the Yuan won't have their entire army and fleet sunk to the bottom of the sea). But keep him focused on Japan so that he doesn't ruin the empire by attacking Vietnam in the meantime like he did OTL. That'll help things along at least a bit.

Second invasion probably would've been a bust either way. The Japanese had a while to prepare coastal defenses and the Yuan were running out of steam due to bashing their head on Vietnam over and over.
 
I am in the works of trying to make a post-Genpei War timeline that sees Japan stay unified (no Sengoku period). The main PoD being a successful Mongol invasion that turns Japan into a client state, and thus weakens the Daimyos.

However, both invasions were tremendous failures, the first barely even approaching Japan at all.

What would it take for the Mongols to, at the very least, force peace terms upon Japan? What needs to be handwaved, or does it stray too far into impossibility?

I wouldn't say it's the Daimyo getting too strong as it is the Hojo having to defend against the Mongols weakened their finances and saw plenty of displeased warriors. The Mongols themselves would have to be able to fight and hold an archipelago with plenty of mountains and rivers all while either living off the land or having supplies sent via the ship. It would be a costly invasion with little benefit unless the Kamakura surrender and quickly.

The problem with trying to avert the decentralization of Japan that would to the Sengoku period is the fact the Kamakura Shoguns were basically controlled by the Hojo regents from 1199 to the Kamakura Shogunate's fall in 1333. Even then, regents either retired or died or had to deal succession disputes within the Hojo clan itself. It's tough trying to create a centralized state in the 1300's with lots of islands and terrain to go take into account.
 
Top