The term "minor league baseball" refers to a collection of leagues and teams that compete across the United States at a level of competition below the major leagues. As of 2010, minor league baseball has existed for more than 100 years and has produced many notable Major League players.
Origins
Minor league baseball originated on September 5, 1901, when seven minor league presidents founded the National Association of Professional Baseball Leagues. The National Association of Professional Baseball Leagues consisted of 14 leagues and 96 teams.
Early Classifications
In the inaugural 1902 season, minor league baseball was divided into four classifications, which organized teams by skill level. The original four classifications were A, B, C and D. This classification system remained intact until 1912, when class AA was added as a higher level of competition than A.
Growth and Contraction
Minor league baseball expanded to 41 leagues in 1914. However, minor league baseball would suffer from competition from other leagues and the draft for World War I. By 1918, only nine leagues were in operation.
First Playoffs
The minor league baseball playoff system was founded in 1932 to increase competition and pique fan interest in the leagues. In early playoffs, only four teams were involved, with the first place team facing the fourth place team and the second place team facing the third place team. The winners met in a championship.
Color Barrier Broken
In 1946, Jackie Robinson became the first African-American to play in a minor league baseball game during his debut with the Montreal Royals. One year later, he would enter major league baseball with the Brooklyn Dodgers.
Expansion
After the Great Depression and World War II ended, minor league baseball enjoyed a period of growth. By 1949, minor league baseball comprised 448 teams in 59 leagues. That year, minor league baseball attendance reached 39,640,443, a record that stood until 2003.
Restructuring
In 1963, the modern minor league baseball classification system was introduced. This classification system is still in effect as of 2011, and consists of six levels of play: AAA, AA, A-Advanced, A, A-Short Season and Rookie.
Name Change and Continued Growth
The National Association of Professional Baseball Leagues officially changed its name to Minor League Baseball in 1999. Two years later, the league celebrated its 100th year in operation. From 2003 to 2008, Minor League Baseball established a new attendance record every year, culminating in 43,263,740 fans in 2008.



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