There isn't an origin story like the Union's.
Normally, MLS opens the expansion process, selects sites among the applicants and awards those ownership groups a team. However, it was done a little differently in Philadelphia.
The Sons of Ben supporter's group was founded in 2007, without a team to root. Instead, the supporter's group was determined to bring a team to Philadelphia themselves. The group went to games between rivals, the MLS All-Star game and even the MLS Cup, chanting, waving flags and clutching scarves for a city that didn't have a team.
But in 2008, MLS awarded Philadelphia an expansion team, and in 2010, the Union played their inaugural match.