the commissioner of MLS was professing his admiration for San Diego as a destination soccer city metro area. Don Garber, MLS commissioner, has said the same of St. Louis, too, stating that sports teams that leave their hometowns create a vacuum and MLS has a better chance to succeed in those places.
There's an argument to be made that the Seattle Sounders' success is in some part due to the absence of the Seattle Sonics of the NBA. Along the same lines of debate, Atlanta United of MLS has their first season this year and may be able to transfer fandom from the relocated, former NHL Atlanta Thrashers team.
There is a pattern showing up across the American sports spectator landscape. This pattern is becoming more evident, soccer matters and it can win hearts over after they've been stomped on and broken. I expect that after the Raiders leave Oakland for Las Vegas that Oakland will join St. Louis and San Diego in vying for a franchise spot in MLS.
The vitality of the NFL is in flux, according to ESPN. The concussion problems have contributed to lower rates of participation in youth football and a reputation issue is front and center, as well. Famous players have killed themselves due to the lingering effects of concussions. And, recently, Bo Jackson admitted he wouldn't allow his kids to play football. This transition period of tiredness with football's inundation has exposed it's vulnerability to viewership and attendance. San Diego was the proving grounds for how there are less amount of people interested in the sport.
If only the largest (primary) metropolitan areas can support both an NFL team and MLS team, that may mean the rest of the country's next level (secondary) large metro areas could be splintered between the two sports. As it stands now, Baltimore, Buffalo, Charlotte, Cleveland, Cincinnati, Detroit, Indianapolis, Jacksonville, Miami, Nashville (TN Titans), New Orleans, Phoenix (AZ Cardinals), Pittsburgh and Tampa Bay, are all NFL metro areas without an MLS team. (I didn't mention Green Bay, which is two hours away from Milwaukee.) Also, I don't consider Detroit, Miami and Phoenix as secondary large metro areas. These three areas belong on the primary large metro area list, but are presently without an MLS team.
MLS metro areas without an NFL team include Columbus, Montreal, Orlando, Portland, Salt Lake City, Toronto, Vancouver, and San Jose. (An argument can be made against San Jose with the 49ers 20 minutes away in Santa Clara.) It may not be fair to include Canadian cities in the discussion because the NFL hasn't tried to poach a Canadian team away from the CFL (Canadian Football League), but the NFL has played regular season games in Toronto for Buffalo Bills home games.
As metro areas in the U.S. ebb and flow in populations, some cities become candidates for the first time for a pro franchise. Omaha and Birmingham are secondary large metro areas that come to mind. I could easily see Omaha with an MLS team and Birmingham with an NFL team in the future.
The delineation of secondary markets among the two leagues is becoming more and more obvious. Sacramento appears to be a sure thing at some point for MLS, as the city is rolling out the red carpet for pro soccer. Sacramento will try to duplicate Orlando, Portland and Salt Lake City as NBA/MLS cities. The sports city phenomena can also be seen in metro areas without the NBA, but with NFL/MLB teams, like Baltimore, Cincinnati and Pittsburgh (the only one of the three with an NHL team).
In the next level (secondary) large metropolitan population areas in the U.S., the future appears to pit American pro football vs. pro soccer. Sports leagues are all about satiating the sports fan's desire to feel a part of a team's identity. MLS can safely say that it is part of the solution.