In 1900, the National League contracted to 8 teams, and in 1901 the American League joined as the "Junior Circuit" with 8 teams as well. The league remained at 16 teams until 1961.
The 1940s was a tough decade to gauge from a production standpoint, as most players lost at least a couple seasons while serving in World War II. At the top of that list is Ted Williams, who lost three seasons in the prime of his career, yet still managed to finish as arguably the greatest pure hitter to ever play the game.
Fellow outfielders Stan Musial and Joe DiMaggio each served time as well, though DiMaggio was around in 1941 when he posted his record 56-game hitting streak.
Flame-throwing Bob Feller threw a pair of no-hitters during the decade and was probably the decade's most dominant arm. However, Hal Newhouser put up the better all-around numbers and managed to win back-to-back MVP awards in 1944 and 1945.