Original: Starting in 1931 , major league teams began affiliation agreements with minor league teams . Branch Rickey , president of the St. Louis Cardinals , was the architect of the system which exists today , in which most minor league teams are affiliates of major league teams , supplying the Majors with development of younger players in exchange for financial support from the major league teams with which they are affiliated .
Simplified: Minor league teams are used by Major League teams to have a place to put their players who they do not feel are good enough to play in the Major League yet .