Well, one reason might be the fact that billiards is popular in continental Europe. In the early part of the 20th century there were well-known European players. In 1914 some events happened in Europe, and Sayginer's home country for that matter. When pool and billiards were hugely popular in the US in the '20's, things maybe weren't as good there. And then the second war came along and affected all the billiard playing countries probably proportionately worse than the US. Billiards was slipping in the US in the '50's, but you had by far the richest country around in the post war boom. When did Ceulemans come into prominence? Early '60's maybe? OK I wikied him and he was born in 1937 and started winning titles in 1961. So he was too young to fight in the war and obv wasn't killed in it and then grew up in a more peaceful era. So then billiards died in the US and the European billiards playing countries got back to normal life. I don't know how much of an effect the wars had, but IMO it is necessary to look at world events when American dominance in a given era is discussed. As for really gifted players, you just need a population base and the game to be popular, and once in a while a great one will be there. Wars that kill off huge percentages of a population or disrupt life will have an impact on how many great players in any sport will develop. I don't know the casualty numbers, but in glancing at some stats saw France lost 1.4 million soldiers in WWI. Oh, yeah, and the flu epidemic killed 50 million I read. So no wonder the best players for a while were in tthe US, which while we fought the wars and lost people in the epidemic, had an ocean on each side, neighbors that couldn't overthrow us, and more prosperity during these periods. And once the game fell out of favor here, it is no surprise that the best players come from elsewhere.