Considering how the United States embraced the belief of Manifest Destiny, perhaps it’s no surprise that growth in Major League Soccer has been pedal-to-the-medal stuff for a decade now.

The 20-team league recently revealed that Atlanta, Minnesota and a second team in Los Angeles will be coming soon. You can count on Miami, too, depending on your degree of faith that David Beckham and his dazzling smile can finally bullseye that elusive downtown stadium.

Just 10 years ago, 12 clubs competed for MLS Cup. At that point, a 16-team operation seemed like a worthy target, if a bit ambitious. By 2010, that number had been achieved, so the new target was set at 20 teams.

Boom! Done. So the new goal became 24, where we are if we count Miami. Except that MLS commissioner Don Garber dropped a whopper in March when he said, paraphrasing here, “We ain’t stopping at 24!”

“We will expand this league beyond 24 teams,” Garber said in the spring. “It’s not an ‘if”, it’s a ‘when.’ ”

Expansion seems to have become a bit addictive, driven by escalating expansion fees, the success of the recent comers – NYCFC and Orlando are hardly struggling to sell tickets – the economics of TV contracts and establishment of a larger national footprint.

Those are the obvious influencers of an increasingly aggressive growth strategy. MLS spokesman Dan Courtemanche noted a couple of less obvious drivers at work, too. First is persistent and abundant interest from high level (read: uber rich and influential) perspective owners. Unlike the early 2000s, when MLS was essentially recruiting potential owners, the league can now afford to play hard-to-get.

Also, Courtemanche said league officials and owners are happy with the way quality of play continues to improve, even while the league expands briskly.

Such expansion talk is like catnip for MLS fans. But before we spin that wheel (“Who is next? Sacramento? St. Louis? Indy? Austin or San Antonio, anyone?”), maybe there is a better question to ask.

When is enough enough? Put a different way, “How big is too big for Major League Soccer?”

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League officials aren’t ready to talk about further expansion parameters, which they say are just now being mapped out. The subject will run around the table at the next board of governors meeting (this summer’s All-Star game) and a more concrete framework could be hardening by this winter. Best guess: we’ll hear about it around the start of the 2016 season.

For now, league officials are talking only generally about the “whens” and “how manys.” “The United States and Canada are two extremely large geographic areas, with more than 350 million people, and where independent market research tells us there are more than 80 million soccer fans between the U.S. and Canada,” Courtemanche said, right after returning to New York from St. Louis. “Clearly that is enough to support a large Division I league.”

A larger MLS seems like a reasonable idea, but there are a few potential monkeys in this wrench.

First, there is a dark cloud hovering perpetually near all this sunny warmth of expansion goodness: it’s the legacy of the failed North American Soccer League, which closed shop in 1985. Clearly, the world is a different place today, as Garber has frequently pointed out when the scarred history of domestic soccer comes up. The roster of rock-solid MLS ownership bears little resemblance to the disparate collective of NASL owners, a rickety wooden bridge by comparison.

The stadium situation is night and day; 15 MLS clubs play inside soccer specific facilities whereas that number in NASL was … exactly zero. A trio of national TV deals that pay MLS a combined $90 million annually will not make NFL owners jealous, but such a sum would have floored the old NASL ownership crowd.

Still, that fatally breakneck pace of NASL expansion did help create the conditions that led to collapse. So for anyone who knows their domestic soccer history, warning bells will necessarily sound at the hurried pace of MLS expansion.

Aside from the drag of history, there are also competitive issues to sort through, because fan interest could fade when teams enter each season with a mathematically puny chance at winning something significant.

Consider other leagues around the world. The heavies of Europe (England, Germany, Italy, France, Spain) all operate their top divisions with 18-20 teams. Same for Mexico’s Liga MX. Mathematically speaking, it’s easier to win La Liga (or any of those others) than MLS. We all know that’s apples to oranges in actual quality – no disrespect to Kei Kamara, the league’s current co-scoring leader, but he’s no Leo Messi – but you get the point.

The English Championship operates with 24 teams, or same as MLS will reach before pushing that expansion envelope past some theoretical breaking point. But that league (England’s second tier) has two critical advantages in terms of fueling what we might call “mathematical hope.”

First, while the Championship obviously crowns a title taker, there are effectively three winners. The top trio of finishers all gain promotion to the ballyhooed Premier League. That trophy is nice and all, but promotion to the “bigs” is the bigger target.

And at the other end, three sad sacks will drop a division. That makes 21 “winners” in the Championship, including three of those promoted “super winners.” So the scale of 24 teams makes more sense when you take in the bigger picture.

In a 24-team MLS, playoff qualification would be every club’s initial target – but in American sports culture, that’s just the lowest hanging fruit. Twelve teams already make the playoffs and, based on MLS history, that percentage is likely to go up. In other words, as incentive, post-season qualification isn’t much. People want winners, and winners mean “championships,” not first- or second-round playoff exits.

Yes, there are CONCACAF Champions League spots to be gained. And there is a Supporters Shield. But CONCACAF Champions League as a brand remains small potatoes, and Supporters Shield might jingle some keys in Seattle or a few other markets, but it’s still just an honorable mention medal in the American sports psyche.

Think about this: are hockey fans in most markets really so invested in the President’s Trophy chase? Because that’s the NHL’s equivalent to Supporters Shield.

In terms of scale, there is precedent for a larger league in the U.S. sports scene. The NBA, NHL and Major League Baseball operate with 30 teams each. The NFL has 32. Generally speaking, it’s working out well for them, especially in the wildly successful NFL.

Surely, none of that is lost on current MLS owners, most of whom still operate in the red. Franchise fees that have settled in around $75 million or more must look utterly irresistible, even when considering that adding more MLS owners will dilute the escalating TV revenue.

There is also the issue of sufficient talent. ESPN analyst Steve Nicol, who coached the New England Revolution for 10 seasons until 2011, is among those who have wondered aloud whether the current tributaries of development can keep up. Academies are changing that conversation, but some are clearly further ahead than others when it comes to producing truly professional talent.

On this one, there seems to be some wiggle room. There is, after all, literally a world of talent out there. If the NBA or NFL was to increase by 6-8 teams, we could all rightly wonder if the American crop yield could keep pace. In soccer? Well, there’s Central America, South America and Asia, and that’s before we get into the (admittedly more pricey) markets of Europe.

It all deserves thinking through. MLS is in a good place, after all. It’s on the rise in so many areas, and this week’s news of a shiny new stadium in L.A.’s urban core is the latest sign of progress. And as long as the league steps back and actually considers the flip-side of rapid expansion, MLS’ll remain in a good place.

The debate over how-big-is-too-big will just be another reason for us to keep talking about expansion, rather than a real worry about whether the league will survive.