I think you are referring to Sahkalin Island that used to be split between Russian and Japan, at the end of WWII Russia over-ran the Island as part of its support for the US efforts in the Pacific, and kept it.

I've been there and its quite wild on the whole, a giant box of natural recourses just awaiting exploitation, very beatiful. Used to house a great many prison camps, some of which are still visible from the train as you move up the island.

Japan definately wants it back, the oil potential is quite large.

Cheers

Sledge