From BR Bullpen
In 1948, Bowman put out a 48-card set in black and white, with one piece of gum and one card in each one-cent pack. In 1949, Bowman issued a 240-card color set, the ancestor of all modern card sets. Bowman also issued a 36-card Pacific Coast League set. In 1950 Bowman had one-year monopoly on baseball cards (Leaf produced cards in 1948-1949, and Topps started in 1951).
Topps and Bowman competed for rights to players for their respective sets until 1955, even including court battles, which explains why some players are featured in one set and not the other, and why sets would be rounded off with the addition of cards featuring coaches or players whose big league career would only consist of a cup of coffee or two. In January 1956, Topps bought out Bowman, leaving a monopoly for Topps until Donruss and Fleer came along in 1981. Topps revived the Bowman name in 1989.