Relegation is a system of promoting minor league teams to the major leagues, and demoting failing major league teams to the minors, used in Europe.
It's a great system that America should adopt for it's sports leagues. However, it'll never happen.
In relegation systems, there is full integration from local, town level teams, up to city, region, and national teams. Weekend semi-pro teams are in the same system as professionals; teams on each level support themselves. There are many semi-pro levels at the bottom, and the best teams in each division move up at the end of each season, replacing the worst teams, who move down.
Some amazing things have happened in relegation systems. Local teams have gone up through the leagues every year, to eventually become professional, build a stadium, and be a major, famous, national team. Pro teams with bad management have fallen to the minors and had to fight their way back up, or die out.
In US sports, the minor leagues are all fake - the teams aren't really playing for anything beyond the individual benefit of the players. Players contributing to a championship doesn't mean anything - it's all about getting noticed as an individual, and being taken to the next level yourself, leaving behind your teammates.
In relegation systems, individuals do move around a lot, but wherever you are for the season, the team you're playing for really does care about what happens - if they win it all, the championship will be worth something to the team and managers, since they're local & personally involved with the team, not just working for a distant top league owner. At the end of the year, it's possible for a team to keep its best players, rather than have them taken away.
It makes league finals more interesting, since promotion makes a big difference in tv & ad revenue, and it also makes losing teams try harder, to avoid relegation - which is bad for the individual players, and also for the team.
Teams can start anywhere there is support - since minor league teams support themselves (they're not slave puppets like MLB/NBA minor league teams), sometimes one of them will pull together a really good team, get enough fans to make enough money to improve themselves, and break into the majors.
This would solve baseball's problem of having teams in tiny markets, and always having to change the rules/management/pay/draft pick structure to artificially make them competitive. With relegation, these teams would just be demoted to minor league teams (where they would be really competitive) - fans would still be able to watch great games, which would mean something now. Teams would compete with others from more evenly sized markets. We would not have this ridiculous movement of teams from city to city - dying or failing teams would just be demoted, and if there was a city that needed a team, they would naturally appear to meet the market.
In big cities, there could be just as many teams as the market would support - if someone wanted to start & put money into a minor league New York team, they could, in hopes of winning the minor league & being promoted to the majors.
This would also take care of the really stupid problem introduced into the MLB/NFL where the top league is expanded every year. Since there would be competitive games for these smaller markets anyway, there'd be no need to promote them to major league level if they couldn't compete.
The reason US sports are so desperate to expand the leagues is because the minor leagues are so meaningless - they're barely sports teams at all, since there are no incentives for them to behave with any team cohesion, and because they have no individual power to hold onto players at the end of the season. They can't make money because they're not giving fans anything like what they want.
In the US system, no matter how many times someone beats the Brewers, they're still going to be around next year. This is bad for them and bad for everyone. Let them die as a major league team, until they deserve it.
It's just too risky to change something worth this much.
People would go watch a lot more sports, if minor league games meant something. Making minor league teams interesting would increase the size of the pie for all sports - there'd be better local sports to go see, playing for them would be meaningful even if you weren't in the pro track, and since they would be more local, interest & support for teams would be more real. At least at the lower levels, most players would be from the area, and would be able to play for a team they knew growing up.
One extra benefit is that teams wouldn't have stupid names, since they would all have come from humble origins, without budgets to think of gimmicky names.