How the supporter culture and following of MLS teams led to the creation of one of the three main trophies & the eventual expansion into 3 new teams.

Sources: 

A History of the Supporters Shield by Ryan Gates for Stumptown Footy

https://www.stumptownfooty.com/2011/2/15/1995978/a-history-of-the-supporters-shield

A Pacific Passion Play by Grant Wahl for SI

https://www.si.com/vault/2011/05/23/106070650/a-pacific-passion-play

https://web.archive.org/web/20071012230838/http://seattletimes.nwsource.com/html/soccer/2003941033_sounders11.html

https://www.sounderatheart.com/2019/8/15/20805034/sounders-new-ownership-changes-faq

https://www.theglobeandmail.com/sports/soccer/whitecaps-invisible-owner-casts-large-shadow/article573189/

https://www.cbc.ca/sports/soccer/mls-expected-to-announce-vancouver-expansion-team-1.821469

https://www.timbers.com/post/2007/05/22/timbers-introduce-new-owner-merritt-paulson-0