based on what? volume? bitflyer has zero trading fees, just like chinese exchanges once did a year ago. back then, we all considered china to be the market leaders based on their volume. it turns out the volume was just fake/churned.

and indeed, russia seems to be behind much of the world in regards to BTC and blockchain technology.

also, there are lots of US traders on sites like bitstamp, bitfinex, poloniex and bittrex. determining which country is dominant in trading activities is very difficult because of international exchanges.