Actually, we let the Canadians play.... When the first Canadian team became a major league team, that's when they started calling it the "WORLD's series" but it was only USA and Canada, hardly the whole world.... Right now, there's only one Major League team in Canada, however (the Toronto Blue Jays - twice World Series Champs).
Of course, baseball is played in many other nations; it's huge in many Caribbean and Latin American nations, in Japan, in South Korea, in Italy and elsewhere. Until recently, it was in the Summer Olympics. There have been International tournaments but I think those organizations are all defunct now. So yeah, there is no international playoff.
Side note that for LITTLE League, it really is very international. And the Little League World Series reveals that.