How many countries take part in the baseball world series?

Two countries take part in the baseball World Series, including USA and Canada.

Just one typically, the United States, but if the Toronto Blue Jays are involved, then it's two.

Municipalities, not countries, play in the World Series, and just two at a time take part,

One at the Major League and College World Series. But the Little League World Series includes many countries.

US, but there are baseball farms in Latin America and Japan where some of the players were grown

Two (United States and Canada).

You might be thinking of the World Baseball Classic. The World Series does feature the world's best players, however. 

two.....but the players represent the best from dozens of countries...

Zero.  It's not an international competition.

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