Why the Russian, and some Eastern Europe nations, like Serbia, Croatia...are doing so good at tennis? They've?

They play a lot of tennis in those countries. Most of those countries play soccer and tennis. In the US so many athletes play other sports. Russia is a big country with a lot of people, but places like Slovakia and Serbia turn out top players too. Andy Murray is good for England and they have some really good young women players with Naomi Broady and Laura Robson who could be very good in the next few years.