The aggressively-improving American League was rejected as an equal major league by the established National League. Although there were multiple major leagues more often than not in the course of organized baseball over the latter half of the 19th Century, at this juncture the NL felt it was the sole top circuit in the game, and it was especially irked that the AL was ignoring the National Agreement to compete head-to-head in NL cities like Baltimore, Philadelphia and Washington, D.C.
How did this affect the White Sox, a newly-formed AL team relocating from St. Paul? The 1900 pennant, the first awarded by the new league, was won by the White Sox, whose 82-53 record was 4 1⁄2 games better than the Milwaukee Brewers. But it, along with the records of the 1900 players, are not consider “major league”; Baseball-Reference, for example, begins its White Sox franchise history at 1901, the first year the AL was regarded as “major.”
However, the White Sox had just four of 28 players without prior major league experience, and half of the players cut from the National League (the circuit had shrunk from 12 to eight teams for 1900) ended up in the AL, legitimizing its major status. And before the season had even begun, the Chicago Tribune observed that “the American League is not, after all, much behind the old, cumbersome National League.”
The 1900 triumph was the first pennant won by a Chicago team in 14 years.
The White Sox, mostly intact and even bolstered from 1900, went back-to-back in winning the AL pennant in 1901, the first season the AL was considered a major league. In fact, Frank Isbell, Roy Patterson, Ed McFarland played on the 1900 and 1901 pennant winners and 1906 World Series winners.