The results of a professional tennis tournament read like a United Nations roll call. Never before have so many countries been represented at the sport's highest level. In July, 26 countries had at least one player in the WTA top 50. The ATP figure was 21 countries.

This diversity is noteworthy, given the history of tennis. Perhaps fitting for a so-called country-club sport, the game was often the domain of the few. Tennis has its roots in France although it was England that gave us the modern form of the sport. Both countries have had eras of prominence and the United States has always had a strong presence.

Then there is Australia, where players produced by that relatively sparsely populated continent, particularly in the 1950s and 1960s, could fill a hall of fame by themselves. Not content to give us one superb player at a time, Australia often produced them in pairs - Mal Anderson and Ashley Cooper; Lew Hoad and Ken Rosewall, John Newcombe and Tony Roche.

'Russia's former president Boris Yeltsin was a fanatical supporter and the country has become a tennis super power'

As a boy I thought the Davis Cup was a competition between the United States and Australia. I thought that way because...well, it always was that way (it should be pointed out that in those days the defending country did not have to play any rounds until the final). In the 2005 Davis Cup final, Croatia (population 4.8 million) defeated Slovakia (5.2 million).

So why has there been an international explosion?

•  International travel is easier. For much of the 20th Century only the best players played abroad, and infrequently at that.

•  Success breeds success. Once a player from a certain country becomes established on tour, the path is cleared for others. Coaching and facilities are upgraded. Young players have a hero to emulate and the belief that they, too, can make it.

• * A single player can spark a tennis boom. Bjorn Borg was such a player. Sweden produced Stefan Edberg, Mats Wilander, Joakim Nystrom, Anders Jarryd and Henrik Sundstrom in Borg's wake.

•  The revolution can come from an unlikely source. Russia's former president Boris Yeltsin was a fanatical supporter and the country has become a tennis super power, especially their women, aptly labelled by Sports Illustrated  writer Jon Wertheim 'the former Soviettes'.

•  There is great financial opportunity. Tennis was primarily an amateur sport until 1968. The big money wasn't there until much later.

•  Tennis would appear to hold a greater attraction for younger women. Despite the increased availability of sports for women throughout the world, their opportunities are fewer than those for boys. Women's tennis offers greater pay cheques, on court and off, than most, if not all other sports. And they can demonstrably maintain their femininity. A shot putter, not so much.

Whirlpool's WTA fantasy league recently concluded its first season (2007 is divided into two seasons). Among the winners were people from Great Britain, Philippines, Italy, Thailand, and The Azores. Indeed, tennis is an international sport.