Thanks for posting the game. It's always fun to see how someone else plays.
I can see the culture problem with the position. Your entire empire is spread out, almost in two pieces, with your old lands and your recent acquisitions from Russia. The people in the West probably feel the the people in London, a capital on the far Eastern edge of the world, don't really understand their problems, or provide a fair share of the benefits of the central government. Your rule is tolerated, but the people still remember your ruthless occupation and bide their time. They are new to you culturally but are surrounded by very old, venerable cities of Russia and China.
(As an example, Pakistan, India and Bangladesh used to be one country, as result of colonialism, but were culturally and geographically split. Eventually, they split politically as well. )
Kyoto, on the other hand, sits astride the Japanese Empire.
This cultural position is very tricky indeed! This is a good example of how some positions are inherently unstable. You might consider taking out old France, as it is still relatively low culturally.
Cavalry may be the only way to consolidate your gains.
I'd be interested in knowing how it turns out.
