Major League Soccer's 20th season is down to four teams. And when they begin their conference finals on Sunday, there are plenty of intriguing storylines.

Much attention will be paid to the youthfulness and good soccer displayed by all the remaining contenders – the New York Red Bulls, Columbus Crew, FC Dallas and Portland Timbers. And there will be questions asked about the fact that, at a time when the league has imported more star power for more money than ever before, none of the last teams standing have a genuine soccer star on their rosters. They are teams that were built shrewdly, eschewing the high-priced household names and opting for balance instead. And balance beat big names this season.

[ MLS Cup Playoffs: Columbus Crew vs. N.Y. Red Bulls | Portland Timbers vs. FC Dallas ]

But there's a bigger and perhaps more important story that hides along the sidelines. And that's the rise of the American soccer coach. Each remaining team employs a young, homegrown manager, who played in MLS and is either on his first or second professional head coaching job.

New York's Jesse Marsch is 42 and played in the league for 14 years. His last job was as Montreal Impact coach, in its inaugural season. Oscar Pareja, 47, is Colombian but has been in the United States for almost two decades. He spent eight seasons in MLS – 7½ of them with FC Dallas. He then ran Dallas's youth academy before returning to manage the senior team after a stint with the Colorado Rapids. Caleb Porter, 40, built the University of Akron into a juggernaut after injuries ended his MLS playing career and then took over the Timbers. Gregg Berhalter, 42, is the only one to have worked abroad, for Hammarby in Sweden, and is now in charge of the Columbus Crew.

If this dominance by American coaches – or honorary Americans, in Pareja's case – sounds anecdotal and a tad flukey, it isn't.

The final four of managers underscore a larger trend. Seven of the eight managers in the conference semifinals were young and homegrown, which is to say that they either played in the league and hung around or got their coaching start in MLS.

In fact, of the 23 managers employed by an MLS team at some point in 2015, 17 were active in the league as players, and none for fewer than three seasons. A full 15 of them were on their first head coaching jobs in the professional ranks. And 18 managers had never managed elsewhere than in MLS – and of the five that did work in other professional-level jobs, Bruce Arena and Frank Yallop only managed the U.S. and Canadian national teams, respectively.

View photos Portland coach Caleb Porter says it's vital to know the league. (AP Photo) More

Porter has an explanation. "There are times where I think it's one of the toughest leagues to be manager in in the world," he said of MLS. "Because ultimately, it's a league of parity and it's a league where you have for the most part pretty equal budgets outside of the Designated Players. And because of that on any given day anybody can beat anyone."

More than that, though, Porter argues, is the many complications beyond the parity mechanisms. It's the tight budget constraints, the endless travel in a short schedule, the differing climates and altitudes.

"Because of that, it's a very difficult league to manage in," Porter said. "You see with a lot of foreign coaches that come, because there's unique challenges that make it difficult. With all of the young coaches that you've seen recently that have come in and done well, they're guys that know the league. They know how to set up and they're not surprised with the travel and all the challenges that go into it. They get it. They're not frustrated, like some foreign coaches that come in."

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