Question: What kind of group does Birmingham City F.C. and English football league system have in common?

<P0-S0> Birmingham City Football Club ( , locally ) is a professional association football club based in the city of Birmingham, England. <P0-S1>  Formed in 1875 as Small Heath Alliance, they became Small Heath in 1888, then Birmingham in 1905, finally becoming Birmingham City in 1943. <P0-S2>  The team compete in the EFL Championship, the second tier of the English football league system. <SEP> <P1-S0> Birmingham City F.C. Development Squad and Academy are the reserve team and the youth development system respectively of Birmingham City Football Club. <P1-S1>  The reserve team, established in 1879, played in the Premier Reserve League South in the 2009–10 season, but did not enter a league again until the 2012–13 season, when it was placed in the northern division of the newly formed Professional Development League 2, a predominantly under-21 league. <P1-S2>  The Academy, established in its current form in 1999, trains boys in age groups from under 9s through to under 18s. <SEP> <P2-S0> Birmingham City Football Club, an English association football club based in the city of Birmingham, was founded in 1875 as Small Heath Alliance. <P2-S1>  For their first thirteen years, there was no league football, so matches were arranged on an occasional basis, supplemented by cup competitions organised at both local and national level. <P2-S2>  In 1888, Small Heath joined the Combination, a league set up to provide organised football for those clubs not invited to join the Football League which was to start the same year. <P2-S3>  However, the Combination was not well organised, and folded in April 1889 with many fixtures still outstanding. <P2-S4>  Small Heath were founder members of the Football Alliance in 1889, and three years later were elected to the newly formed Second Division of the Football League. <P2-S5>  They topped the table in their first season, though failed to win promotion via the test match system then in operation, but reached the top flight for the first time in 1894. <P2-S6>  Since that time, they have not fallen below the third tier of the English football league system, and were promoted to the Premier League for the first time for the 2002–03 season. <SEP> <P3-S0> The English football league system, also known as the football pyramid, is a series of interconnected leagues for men's association football clubs in England, with six teams from Wales and one from Guernsey also competing. <P3-S1>  The system has a hierarchical format with promotion and relegation between leagues at different levels, allowing even the smallest club the theoretical possibility of ultimately rising to the very top of the system, although in practice it would take a team at the bottom levels at least two decades of consistently finishing at or near the top of each successive league to reach the top level, and even then additional restrictions, particularly in regard to stadium facilities, would then come into effect at the highest levels that could prevent a club from being allowed access to the top levels. <P3-S2>  There are more than 140 individual leagues, containing more than 480 divisions.