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Minor leagues are professional sports leagues which are not regarded as the premier leagues in those sports. Minor league teams tend to play in smaller, less elaborate venues, often competing in smaller cities/markets. This term is used in North America with regard to several organizations competing in various sports. They generally have lesser fan bases and smaller budgets.
The minor league concept is a manifestation of the franchise system used in North American sports, whereby the group of major league teams in each sport is fixed for long periods between expansions or other adjustments, which only take place with the consent of the major league owners. In Europe, and many other parts of the world, the football leagues have many divisions below the top-flight as part of the football pyramid. In other parts of the world there is usually either a system of annual promotion and relegation, meaning that clubs have no fixed status in the hierarchy, or there is only one professional league per country in each sport, rendering the major/minor distinction irrelevant.
While there are various semi-professional football leagues, none have any affiliation with the National Football League (NFL). The NFL and its teams have had working relationships with several independent leagues in the past, including the Association of Professional Football Leagues, the Atlantic Coast Football League, and most recently, the league owned-and-operated NFL Europe. In modern times, the NFL has developed players not ready for the active roster through each team's practice squad.
Many consider the Arena Football League to have been a de facto minor league, since several NFL owners had teams in it in the mid-2000s, prior to its bankruptcy and restructuring. Arena football is played under very different conditions, and the AFL had its own minor league, af2, until 2009. Several other independent indoor football leagues that play a similar game exist.
Similarly, the Canadian Football League, though it has developed ties with the NFL in recent years and has moved away from competing with the NFL for talent, plays a visibly different game than the American game, and the two sports favor different types of skills; the CFL arguably holds major league status in its home territory of Canada.
Several minor or developmental leagues, independent of the NFL, have come and gone, such as the recent United Football League and the Fall Experimental Football League, but none have lasted more than a few seasons. On November 27, 2016, it was reported by CBS Sports that the NFL will present formal proposals for a developmental league or in-season academy (with Troy Vincent prepared to make recommendations) in 2017. Vincent stated "We are ready to socialize our findings to the respective committees at the Pro Bowl, Senior Bowl, and combine" he also stated "We have some viable potential options that are ready to share with the Competition Committee, the Coaches Subcommittee and with some of our active and former players", "Our goal is to create a platform that addresses the entire football community--coaches, officials, front office personnel and players--is essential to the long-term sustainability of our game."
Below Major League Soccer several lower-level leagues operate on both sides of the U.S.–Canada border as part of the American and Canadian soccer pyramids. As is standard for sports in both countries, the formal promotion and relegation system is not used, although teams have been informally "promoted" from lower leagues up to Major League Soccer. As of the current 2018 U.S.–Canada soccer season, the second level is the United Soccer League (USL), which will be rebranded as the USL Championship for 2019 and beyond. The North American Soccer League had previously been the second level, sharing that status with the USL in 2017, but major instability in the NASL led to the loss of that league's second-division status and raised serious questions as to its very survival. USL's parent organization, known as the United Soccer Leagues (note the plural), also operates USL League Two (formerly the Premier Development League, or PDL), a semi-professional league that has some age restrictions. The National Premier Soccer League operates at approximately the same level as League Two. While there was no official third-level professional league in 2018, the USL organization plans to launch USL League One at that level in 2019, and another third-level circuit, the National Independent Soccer Association, also plans a 2019 launch.
In 2013 Major League Soccer announced a partnership with the USL which began formal affiliation between some USL teams and MLS teams.  The partnership has continued to deepen; several MLS teams now field their own reserve teams in the USL, and MLS now requires all of its teams to either field a reserve team in the USL or officially affiliate with a separately owned USL team.  No formal relationship exists between NASL and the other leagues; NASL's commissioner has said he believes it will "stay that way for some time". 
Minor league baseball is almost as old as the professional game itself, and at first consisted of attempts to play baseball in smaller cities and towns independent of the National League, the first true major league. Soon, scouts for the National League were traveling to watch minor league teams play and attempting to sign the more talented ones away. Soon Major League Baseball began formal developmental agreements with some minor league teams, while others remained independent.
Since it was first developed in the 1920s by St. Louis Cardinals executive Branch Rickey, the formal developmental affiliations have come to dominate minor league baseball, and the majority of minor leagues are part of the affiliated system. A general decline in minor league attendance occurred following the advent of television; minor league clubs only survived in many markets because their major league affiliations included financial support. The trend began to reverse in the 1990s, as new independent minor leagues began for the first time in decades and have become successful to varying levels.
The National Basketball Association has an affiliated minor league: the NBA G League (formerly called the "NBA D-League"). The now-defunct Continental Basketball Association (CBA) served some of the purposes of a minor league for the NBA for many years. However, there were no direct developmental agreements between CBA and NBA teams the way that there are between Major League Baseball and National Hockey League teams and their minor league affiliates.
The sport with the next most extensive system of minor league teams other than baseball is ice hockey. In North America, between 1988 and 2005, 233 minor ice hockey teams played in a total of 160 cities in 13 minor professional leagues. The vast majority of these teams played in the United States, with only 21 of these teams based in Canadian cities. 123 of these minor professional teams played in the southern United States.  One reason given for the large number of American-based teams is that minor league franchises will frequently move from city to city, and even between leagues.  In contrast, Canadian cities more commonly host major junior teams, which develop teenage prospects prior to their move to the professional leagues.
The American Hockey League is the most prominent of the minor hockey leagues in North America.
Current minor leagues
- American Hockey League (AHL)
- ECHL (formerly known as the East Coast Hockey League)
- Federal Hockey League (FHL)
- Ligue Nord-Américaine de Hockey (LNAH)
- Southern Professional Hockey League (SPHL)
Former minor leagues
- Atlantic Coast Hockey League (ACHL), now part of the Southern Professional Hockey League
- Central Hockey League (CHL), merged into the ECHL
- International Hockey League (IHL), merged into the American Hockey League
- International Hockey League (2007) (IHL), formerly the United Hockey League and Colonial Hockey League, merged into the Central Hockey League
- South East Hockey League (SEHL), now part of the Southern Professional Hockey League
- West Coast Hockey League (WCHL), merged into the ECHL
- Western Hockey League (1952–74) (WHL), merged into the Central Hockey League (1963-1984)
- Western Professional Hockey League (WPHL), merged into the Central Hockey League
- World Hockey Association 2 (WHA2), now part of the Southern Professional Hockey League
All National Hockey League teams have a farm team in the American Hockey League and often share a team in the ECHL. On "the farm" the NHL team will develop young players, occasionally rehabilitate older players who are injured or whose quality of play has slumped. These teams, in turn, have lower-level minor leagues to draw players from and pass players down to. Minor ice hockey leagues should not be confused with Junior or Senior ice hockey leagues. They are different in that minor professional hockey leagues do not have restrictions on the age or experience levels of their players, but Junior and Senior leagues do.
Other sports organizations considered to be minor leagues are golf's Web.com Tour and Symetra Tour, respectively affiliated with the PGA Tour and LPGA; NASCAR's Xfinity Series, Camping World Truck Series and Whelen All-American Series; and various other affiliated satellite tours of other individual sports, including the Challengers Tour of Professional Tennis.
- Association of Professional Football Leagues
- List of top level minor league sports teams in the United States by city
- Minor ice hockey
- Minor League Baseball
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