It was 2008, outdoors at Humboldt Park, and storm clouds were threatening to put a serious damper on Alverno Presents’ annual world music festival, Global Union. Malian singer and guitarist Vieux Farka Toure was halfway through a blistering set when the sky finally opened up and let loose. “That’s it. Everyone’s going to go home,” David Ravel, Artistic Director of Alverno Presents remembers thinking. “But suddenly, all throughout the park, umbrellas began to pop, pop, pop up like wildflowers. I thought, ‘Jesus Christ, these people are staying.’

“My sister was there, visiting from Santa Monica,” Ravel continues, “and afterwards she said, ‘I’ve never seen anything like that. If this had been L.A. people would have gone home.’”

Inclement weather has been just one of the many obstacles Global Union has faced over the years. World politics, visa issues, cancelled flights, and labyrinthine international paperwork have all made the festival—which has played host to artists from all corners of the globe—a particularly tricky one to pull off. But, as Ravel’s sister noted back in 2008, apathetic Milwaukee audiences have never been a problem.

“People keep telling me, ‘Oh, you have to do Global Union! We love Global Union! We expect Global Union!” Ravel says.

On Saturday, September 19 at Humboldt Park, from noon until 6 p.m., that expectation will once again be fulfilled when Global Union celebrates its 10th anniversary. Performing will be West African and Senegalese jam band Aziz Sahmaoui & University Of Gnawa; Polish singer-songwriter and one-woman orchestra Karolina Cicha; Montreal rapper Boogat; and multi-national funk/rap/rock/punk/soul outfit La Chiva Gantiva. Radio Milwaukee’s Marcus Doucette will return as MC, and WMSE’s Paul Cebar will once again spin vinyl between sets. As always, admission is free.

For a festival as popular and storied as Global Union, its beginnings are remarkably humble. “In 2005 I was invited to what was then Madison’s second world music festival,” Ravel says. “I was watching Gogol Bordello—and if it wasn’t Gogol Bordello it was some other Lower East Side Gypsy Punk band—and the lead singer had climbed up on the lighting rig and was hanging from his knees and belting out songs. I thought, ‘This is awesome. I’d like to try something like this.’”

A few months later, in January 2006, Ravel and his then boss, Michael Harryman, were backstage at a show in Manhattan when they were approached by the then head of Chicago’s World Music Festival, Mike Orlove. “‘My name is Mike Orlove and I do the World Music Festival in Chicago and I need there to be a festival in Milwaukee and I want you to do it,’” Ravel remembers Orlove blurting out. “Oh. Uh. Okay,” was Ravel’s response.

Nine months later, the first Global Union was born, becoming part of a loose route of Midwest world music festivals covering Chicago, Madison, Minneapolis, Cedar Rapids, and Bloomington. That route is what made—and continues to make—the Milwaukee fest and others like it possible. Ravel explains: “Take Poland, for example. It’s kind of a big deal for somebody to come over to the Midwest from Poland to do one show. It’s frightfully expensive and inconvenient for everybody. But if you have a route of people doing stuff at the same time, they get to amortize their cost over the route instead of a single show.”

Still, scheduling can be tricky, especially in cities where sports may or may not trump world music. “Madison and Bloomington obviously can’t do anything on a football weekend,” Ravel explains, “so we have to wait for the NCAA to put out their schedule for the year and figure out when the home games are not happening. Then Madison and Bloomington get to choose their dates, and then we get to place ourselves within a two-week window.”

Owing to its status as a world music festival, Global Union has also been at the mercy of world conflicts. In 2013, Nigerian superstars Thal National were forced to cancel their Milwaukee appearance after running into particularly thorny visa issues. “For the visa process, you do your paperwork several months in advance, and then a few weeks in advance you have to have an interview at the embassy in your home country,” Ravel explains. “There was a terrorist alert in North Africa at that time, and the Obama administration shut down all the embassies in North Africa. So nobody could get their interviews and their visas were all messed up.” (Thal National were also set to appear at this year’s fest, but had to cancel once again due to scheduling conflicts.)

Another hurdle for Global Union, at least in the early years, was finding the right mood for a Milwaukee audience. The solution: go big. “We’re in Humboldt Park. We love being in Humboldt Park,” Ravel says. “But we’ve learned, sometimes the hard way, that small and subtle does not work. It needs to big. It needs to be dance-y. It needs to be a party.

“We try to structure an arc to the day,” he continues. “There’s a rising line of action in terms of activity and intensity on the stage. This will be high-energy. This will get people’s pulses and bodies going.”

But why, in a city already stocked with so many high-energy festivals, is Global Union important to Milwaukee? Ravel has a simple answer: “Milwaukee is a very diverse community that doesn’t get to see how diverse it is every day. To make something where the diversity of our community is visually obvious for everyone is really appealing.”

Global Union 2015 takes place—rain or shine—Saturday, September 19 at Humboldt Park from noon until 6 p.m. Admission is free.