LOS ANGELES — When Don Garber took over as Major League Soccer commissioner on Aug. 4, 1999, his league had 12 teams. One, the Columbus Crew, had just built its own stadium. The majority of the other 11 were desperately hanging on to the coattails of NFL teams or colleges. The New York Metrostars played at the Meadowlands; the Colorado Rapids played at Mile High; the Chicago Fire played at Soldier Field; the Kansas City Wizards played at Arrowhead; and so on.

“When the original business came together, there was no plan for soccer stadiums,” Garber says. “They thought that MLS would play in everybody else’s large buildings as a secondary tenant.”

As Garber speaks now, 17 years later, he peers through big round sunglasses towards a stage, some dirt, more than a dozen black and gold shovels, and more than a dozen men posing for photos. Magic Johnson and Will Ferrell are among them. Behind them is a rendering of Los Angeles Football Club’s new $250 million stadium, which will be entirely privately funded.

When Garber took over at the league’s helm, he quickly recognized that the secondary tenant model was less than ideal. It prevented MLS clubs from controlling revenue streams. It preempted any warmth or intimate feel among fans. It led to swaths of empty seats and a forgettable gameday experience.

But not even Garber foresaw a day like Tuesday, when, at Exposition Park in Los Angeles, in the shadow of the Coliseum, the league’s 23rd team broke ground on what by Garber’s count will be the league’s 20th soccer-specific stadium.

“That’s billions of dollars of investment, and lots of support from public figures to help bring this sport to communities,” Garber said Tuesday. “It’s what’s transformed our league.”

Soccer-specific stadiums have defined the last decade of MLS growth — and make no mistake, it is growth, even if it’s been limited.

Garber’s count of 20 stadia is questionable. To get to 20, you have to include at least three of:

• Vancouver’s multi-purpose BC Place, which is also the home of the Canadian Football League’s BC Lions

• Arthur Blank’s Mercedez-Benz Stadium, which will house both Atlanta United FC and the Falcons in 2017

• D.C. United’s current home, RFK Stadium, which now technically only hosts soccer, but was built as a football/baseball stadium (and is a run-down dump)

• United’s future home, D.C. United Stadium, which is still nothing more than renderings but is expected to open in 2018

Nonetheless, the proliferation has been both gradual and exceptional. There are currently 14 active soccer-specific stadiums — 15 if you count BC Place. Of the 15, 12 hosted their first MLS season in the eight-year period from 2005 to 2012.

As the league continues to expand toward its goal of 24 teams by 2020, and eventually 28 (at least), a soccer-specific stadium has almost become a prerequisite for prospective franchises. There are some exceptions — New York City FC, for example — but Orlando City, Minnesota United, Atlanta and LAFC will all have swank new homes. David Beckham’s Miami-based club can’t join the league until it secures a site for its arena.

In a way, this stage of MLS’s evolution is near complete. When Garber talks about the league’s transformation, he’s talking about the live, in-stadium experience. It’s undergone a full-fledged makeover that’s touched nearly every one of the league’s cities.

And, crucially, fans have bought in. In 2000, Garber’s first full year in charge, average attendance sunk to a new low of 13,756 per game. Fifteen years on, that number grew to 21,574; the last-place Colorado Rapids, who owned the lowest 2015 average among 20 clubs, drew 15,657 fans per game — nearly 2,000 per game more than the league average 15 years ago.

But as billions of both public and private dollars have been poured into the stadium projects, full-fledged growth remains hung up on one damning fact: Nobody watches MLS on TV.

Owners and league officials like to portray growth as inevitable. “The MLS in general is on a rocket ship,” LAFC president Tom Penn said Tuesday. “It’s on such a rise up right now, in popularity, in top-of-mind awareness.”

But that top-of-mind awareness is all localized. Penn has lived in Portland. He’s seen the foremost example. That city is infatuated with the Timbers. For this weekend’s game against Seattle on Sunday, fans will camp out overnight to get preferable seats. The atmosphere will outshine most European and South American games.

But will anybody in Nashville, Tenn., or Cincinnati, Ohio, or Phoenix, Ariz. really care?

TV ratings suggest they won’t. This past Sunday’s game between the same two teams drew just 164,000 combined English and Spanish language viewers. That’s fewer than a Motocross event on NBC Sports Network that same evening, and more than three times fewer than Sunday’s most popular Liga MX game.

MLS TV ratings remain stagnant. Even though the number of national TV games has more than doubled over the past decade, and the current TV contract is its most lucrative yet, the league drew more viewers per regular season national telecast in 2007 than it did in 2015. The 2015 MLS Cup final between Portland and Columbus was one of the least-watched league finals ever.

Penn’s “rocket ship” can’t take off until TV ratings improve. TV ratings likely can’t improve until the level of play spikes. The level of play won’t spike until the league’s salary cap spikes or disappears. (It won’t rise above $4.2 million before 2019, though there are all kinds of convoluted rules that allow teams to surpass it.) The salary cap, however, likely won’t disappear until owners’ profits increase; and profits can’t increase significantly until TV ratings do.

So it might not be until all the soccer-specific stadiums are in place and all expansion teams have settled that we see whether MLS can truly mushroom as a national and international product. Perhaps then, with so many investments in infrastructure already made over the past decade, the league and its owners will be willing to take a risk and let the cap explode, thus kicking off the next stage of MLS’s evolution.