Who were the 16 major league baseball teams in 1900-1953's?

I think you're referring to 1901, when baseball as we know it was born. The uni-league play was still in effect in 1900, with the defunct Brooklyn Superbas (who became the Brooklyn Robins in 1901 and became the Brooklyn Dodgers later on) winning the 1900 world series. There was no 1901 or 1902 world series, but the teams were pretty much in effect then.

1. Philadelphia Athletics (Kansas City/Oakland Athletics)
2. Chicago White Sox
3. New York Yankees
4. Boston Americans (Boston Red Sox)
5. Pittsburgh Pirates
6. Cincinnati Reds
7. New York Giants (San Fransisco Giants)
8. Chicago Cubs
9. Detroit Tigers
10. Brooklyn Robins (Los Angeles Dodgers)
11. Cincinatti Reds (the oldest team in professional sports)
12. Cleveland Indians
13. Washington Senators (Minnesota Twins)
14. St. Louis Cardinals
15. St. Louis Browns (Baltimore Orioles)
16. Boston Beaneaters/Braves (Atlanta Braves)