Country, population
USA, 334M
Mexico, 129M
Japan, 124M
South Korea, 51M
Canada, 40M
Colombia, 52M
Venezuela, 28M
Cuba, 11M
Dominican Republic, 11M
Panama, 4M
Those are the countries where baseball is a major sport. The total population is 784M which gives the USA 43% of the population of baseball playing countries but 74% of the MLB population. We aren't as crazy for baseball as the Dominican Republic but we're producing more than our share of baseball talent.
Those stats include Puerto Rico as part of the USA (because it is).