English rolled into Scotland in horses, the Japanese rolled into Korea in tanks. Sure, after 400 years there was a "political" union, but generally when your charge of a place for a dozen human lifespans, you can generally do whatever you want. If Japan had held onto Korea for a couple of centuries, i'm sure we would've eventually seen an fully entrenched United Kingdom of the Far East, maybe with your very own Princess Diana.
Or your own Jappo-Korean Pippa Middleton, at least:
http://www.malcolmcoles.co.uk/blog/wp-content/uploads/2009/04/arse-pippa-middleton.png