Expansion of Major League Soccer

The expansion of Major League Soccer has occurred several times since the league began play in 1996. Major League Soccer was established as the top level of professional soccer in the United States in 1993 with 10 teams and began play in 1996. It has expanded several times since 1998 into new markets across the United States, and since 2006, into Canada.

MLS is currently at 22 teams, with plans to expand to 28 teams. On January 31, 2017, MLS announced Charlotte, Cincinnati, Detroit, Indianapolis, Nashville, Phoenix, Raleigh/Durham, Sacramento, San Antonio, San Diego, St. Louis, and Tampa/St. Petersburg as its official expansion candidates. The league added its 21st and 22nd teams for 2017: Atlanta United FC and Minnesota United FC. Additionally, MLS plans to add Los Angeles FC in 2018 and a Miami team, pending a finalized stadium plan. The current bidding for the 25th and 26th expansion teams are planned to join in 2020 with expansion fees of $150 million. Expanding and establishing a bigger national footprint is seen as essential to securing television rights fees needed to reach MLS's stated goal of becoming one of the top leagues in the world by 2022.

Major League Soccer considers several criteria when determining where to award expansion franchises:

MLS expansion got off to a mixed start in its initial years. MLS began playing with 10 teams in 1996, grew to 12 teams in 1998, but put expansion plans on hold and then eliminated two teams following the 2001 season to return to 10 teams.

Major League Soccer was established in 1993, as part of an agreement with FIFA that the United States set up a professional first division to gain the right to host the 1994 FIFA World Cup. No successful professional outdoor soccer league existed since the North American Soccer League folded in 1985. Due to rapid over-expansion and poor franchise placement, the NASL collapse led future MLS leaders to be extremely cautious of establishing new franchises.

...
Wikipedia