Eliminated the 'reserve clause', allowing free agency that created competition and disdain with the AL and NL.
Sputtering through two short seasons, the league was the first to introduce free agency and multi-year contracts.
The "Junior Circuit" claimed Major League status 25 years after the formation of the NL.
Originally a minor league in 1885, evolved into a major league that eventually became the modern American League.
Known as "The Brotherhood" league, it was formed around players from the National League's first players' union.
The league president's favoritism toward his own St. Louis franchise doomed the league from the beginning.
Became a significant force in baseball by playing on Sundays and allowing sales of alcohol, unlike the NL.
The "Senior Circuit" is the world's oldest professional team sports league still in existence today.
The league included most of the pro clubs and highest caliber players of its time, paving the way for the origin of the NL in 1876.
The first organization governing professional baseball and establishing standard rules across the national sport.
All-black league used as a distraction while the Dodgers formulated and end to segregation in baseball.
Organized by franchises located in the Midwest as competition to the Negro National League's eastern teams.
Owners of 7 negro league teams ratified a constitution and organized a successful second Negro National League.
Eight teams joined in an ill-fated attempt to organize Negro baseball during the Great Depression.
Several established teams joined the NSL, mainly from the collapsed Negro National League a year prior.
An attempt to create a league by five surviving teams from the failed Eastern Colored League.
Formed by several eastern teams that broke away from the midwest-based Negro National League.
The first organized and financially successful professional Negro baseball league.
Formed to protect teams from unreliable managers, schedules, and rosters of past independent clubs.
League composed of a mix of white, Cuban and Negro league baseball teams in Pennsylvania, New Jersey and Delaware.
The second attempt to have a league consisting of all-black teams, predating the Negro National League by over three decades.
The first formal black league included teams from Atlanta, Charleston, Jacksonville, Memphis, New Orleans and Savannah.
Segregation and racism forced most African American players to join independent travelling teams.
Founded as the Japan Occupational Baseball League, often referred to as "Japanese baseball", or locally, Puro Yakyū (プロ野球).
Originally called the Korea Baseball Championship, is the highest level league of baseball in South Korea.
Gained popularity when Taiwanese little league teams won numerous World Series championships in the 1970s and 1980s.
The league is the owner of each team and players are paid in a number of tiers based on experience level.
Established by TV tycoon after dispute over broadcasting rights. The CPBL absorbed the TML in 2003.
Professional baseball league under the administration of Chinese Baseball Association, founded in 2002.
Disbanded in 2012, but through universities and other private organizations, baseball continues to thrive.
Originally founded as Liga de Béisbol Semiprofesional de Puerto Rico (LBSPR) as a semi-professional league.
Following the world championship in Havana, integrated baseball in Venezuela attracted ball players from the Caribbean and the U.S.
Signed a large amount of players from the Negro League of the with large salaries by Dominican owners.
Previously known as Sonora Winter League and Sonora-Sinaloa League before adopting its present name in 1970.
Winter baseball league composed of 4 teams, all in the Mexican state of Veracruz.
Also known as the Colombian Winter League, plays during three months during the MLB offseason.
Operated from 1948-1972 as Panamanian Professional Baseball League. Restarted as 'Probeis' in 2011.
Due to economic difficulty, the league was shut down in 1967 and was re-established in 2004.
Government run, formed after the dissolution of the Cuban League in the wake of the Cuban Revolution.
Integrated with black, white, and Cuban players. Dissolved after Fidel Castro decreed abolition of professional baseball.