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 end of the 1910s saw the end of the dead-ball era, as Babe Ruth ushered in an offensive boom with a record 29 home runs for the Red Sox in 1919, his final year in Boston.
Before Ruth claimed the crown of game's biggest star, however, the decade belonged to Tigers center fielder Ty Cobb. He won the batting title in all but one season for the decade and never hit lower than .368, including a .420 mark in 1911.
On the pitching side of things, two of the most prolific arms of all time, Walter Johnson and Pete Alexander, dominated the rest of the field. However, it was pitchers-turned-outfielders Ruth and Smoky Joe Wood who may have been the decade's biggest stars, at least at one point or another.