Soccer has been an International Sport for what seems like forever. When teams here in the United States are starting to breakout and schedule League games in Mexico and London like the NFL. The NCAA is taking football down under, and Baseball most recently played a game in Cuba. Soccer has been borderless for much longer.
While popularity for the sport is gaining traction here in the US with MLS, Eurpoe has long been the place to be when it comes to Soccer. Inter Milan has been around for 108 years, Paris Saint Germain, just over 45 years.