I had a nice turnset! Pretty lucky.
Pre-turn: changed a lot of useless entertainers to tax collectors or even citizens sometimes.
Turn 1: moving troops and workers.
Turn 2: transported cavalries and infantries from the core cities to the Japanese continent.
Turn 3: Discovered Mass Production. Next:
Motorized Transportation 

Turn 4: Declared war on
Japan. Captured
Matsuyama,
Edo, and
Suo.
Turn 5: They recapture
Edo for less than one turn. I take it back, and conquer
Nagoya and
Kagoshima.
I was in a hurry and didn't move the workers for the next turn... Next player will have to do this instead of me.
Also the cities
Osaka,
Izumo,
Hakodate and
Yokohama should fall next turn without any problems. I have a SoD of Infantries and Artillery near
Osaka, I have 6 cavs near
Izumo, an army of cavs and a cav near
Hakodate, and an army of cavs and a cav near
Yokohama (should be enough, I don't think they have more than 2 Musketmen in each of those 2 cities).
To the next player: prove us that you are good and take out 4 Japanese cities in the first turn, then you will probably be able to finish them in your turn set, since they will have 2 cities left.
I don't remember, what victory are we going for? If we are going for something military then we should go for the Iroquois next, since they are close to our continent (if we approach them from our easternmost part), and they are arrogant enough to demand a tech from us saying that we exist because they want to.
Good luck!
Here is a pic of the Japanese front. I made some plans, but they are obvious.