Big Three television network

The Big Three television networks are the three major traditional commercial broadcast television networks in the United States: the American Broadcasting Company (ABC), CBS (formerly known as the Columbia Broadcasting System) and the National Broadcasting Company (NBC). Beginning in 1948 until the late 1980s, the Big Three networks dominated U.S. television.

The National Broadcasting Company and Columbia Broadcasting System were both founded as radio networks in the 1920s, with NBC eventually encompassing two national radio networks, the prestige Red Network and the lower-profile Blue Network. They gradually began experimental television stations in the 1930s, with commercial broadcasts being allowed by the Federal Communications Commission on July 1, 1941. In 1943, the U.S. government determined that NBC's two-network setup was anticompetitive and forced it to spin off one of the networks; NBC chose to sell the Blue Network operations, which became the American Broadcasting Company.

All three networks began regular, commercial television broadcasts in the 1940s. NBC and CBS began commercial operations in 1941, followed by the DuMont Television Network in 1944 and ABC in 1948. The three networks originally controlled only a few local television stations, but they swiftly affiliated with other stations to cover almost the entire United States by the late 1950s. Several of these stations affiliated with all three major networks and DuMont, or some combination of the four, in markets where only one or two television stations operated in the early years of commercial television; this resulted in several network shows (often those with lower national viewership) receiving scattershot market clearances, since in addition to maintaining limited broadcast schedules early on, affiliates that shoehorned programming from multiple networks had to also make room for locally produced content. As other stations signed on in larger cities, ABC, NBC, and CBS were eventually able to carry at least a sizeable portion of their programming on one station.

...
Wikipedia