There are a lot of major storylines heading into Saturday's game between the Union and Seattle Sounders at CenturyLink Field. This one might not be the biggest, but I think it's definitely worth spotlighting.

Philadelphia Union midfielder Freddy Adu and Seattle Sounders forward Eddie Johnson have traveled around the world in their soccer careers. On Saturday, they will be reunited on one of Major League Soccer's biggest stages.

So let's take a trip in the American Soccer Way-Back Machine, shall we?

When Adu made his professional debut in 2004, he was not the only rising American star who commanded the spotlight. Johnson rocketed to prominence in his fourth year as a pro by scoring 12 goals in 26 games for the Dallas Burn.

(2004 was the last year in which the team now known as FC Dallas was called the Burn, in case you're wondering.)

Johnson's size, pace and power as a 20-year-old earned him the nickname "Grown-Ass Man" from fans. It also earned him a place in the U.S. national team, which led to a memorable streak of five goals in three games in that year's World Cup qualifying round.

Johnson's club form tailed off in 2005 and 2006, though he continued to regularly play and score for the national team. But in 2007, the Florida native shot back into the spotlight by scoring 15 goals in 24 games for the Kansas City Wizards.

That drew the attention of English Premier League side Fulham, which signed Johnson to a contract in January of 2008. Coincidentally, Johnson's move across the Atlantic took place during the same European season in which Freddy Adu transferred from Real Salt Lake to Portuguese club Benfica.

(Adu's move technically happened in the summer before the season started, but bear with me.)

The moves came with much fanfare, given the big stages on which Fulham and Benfica play. But both players failed to crack their clubs' starting lineups on a regular basis. Johnson only made 19 appearances for Fulham and never scored. Adu made just 11 appearances for Benfica, though he did score twice.

Both players were loaned out to other clubs for the 2008-09 European season. Johnson went to Welsh club Cardiff City, then of the English second tier, where he played 30 games; and Adu went to French club Monaco, where he only managed to get on the field nine times.

After that season, each player returned to the respective clubs that held their rights - only to be loaned out again. Adu was loaned to another Portuguese club, Belenenses, but the one-year deal was cut short after six months. In January of 2010, Adu was loaned to Greek club Aris Thessaloniki.

It just so happened that literally days earlier, Fulham sent Johnson to the very same club. It remains one of the great coincidences in the modern era of American soccer that two Americans ended up together at a mid-table Greek team for six months.

Stranger still is this fact. Of the 15 league games for which Johnson and Adu were both on Aris' roster, they were only on the field together four times.

In the first of them, January 31, Adu assisted on a Johnson goal in a 2-1 loss to Skoda Xanthi. Skoda's goalkeeper in that game was current Sounders netminder Michael Gspurning. I am not kidding. Here's the proof:

Adu and Johnson played together for Aris three more times: February 14, February 21, and March 28.

(If you want to be really particular about it, there was a fifth game in which Adu and Johnson both played, a cup tie on May 17. But they didn't play together, as a double-substitution took Adu off the field at the same time that Johnson entered.)

It would be enough of a bar-room legend if the story ended here, but it doesn't. Johnson and Adu were loaned out yet again during the 2010-11 season: to English second-tier club Preston North End and Turkish second-tier club Çaykur Rizespor, respectively.

Adu scored four goals in 11 games for Rizespor, which got the attention of U.S. national team coach Bob Bradley. That led to a call-up for the 2011 Gold Cup, and Adu surprised a lot of people by being one of the U.S.' best players in the tournament.

Within weeks of Adu's two-assist performance, rumors started swirling about a potential return to MLS. The final hint came when the U.S. played Mexico at Lincoln Financial Field in August. Adu was very hard to get a hold of in the run-up to the game, and on the rare occurrences when he did speak his lips were sealed about his future.

The very next day, though, the secret got out: Adu was indeed coming home, and to Philadelphia specifically.

While Adu was starting to rebuild his career at Rizespor, Johnson was struggling at Preston. He only played 11 games for the club, then decided he'd had enough. At the suggestion of another former U.S. national team player, DaMarcus Beasley, Johnson returned across the Atlantic to try to sign on with Beasley's Mexican club, Puebla.

Johnson worked out with Puebla for a few weeks, but never signed a deal. At that point, it was late December of 2011, and there weren't many places for him to turn. So he turned to one place he knew he could go: Major League Soccer.

Seattle Sounders coach Sigi Schmid had seen plenty of Johnson's MLS career when coaching the Los Angeles Galaxy and Columbus Crew. Just as Bob Bradley believed that Freddy Adu still had it in him to deliver for the U.S. national team, Schmid believed that Johnson still had his goal-scoring instincts.

There was a problem, though. The Montréal Impact held Johnson's rights, due to the allocation process by which U.S. national players enter MLS from abroad.

But Schmid got his man, and in blockbuster fashion. The Sounders gave up Seattle cult heroes Michael Fucito and Lamar Neagle, sparking outrage in the Emerald City and a lot of questions across the league.

Schmid was asked the same question that Peter Nowak was asked when the Union acquired Adu: Are you crazy, or crazy like a fox?

Neither Johnson nor Adu has definitively provided an answer yet. Both players needed time to get back into game shape, and to overcome injuries suffered in training.

In recent weeks, though, the lights have started to flicker on once again. Adu has finally emerged as the creative force the Union have needed, and Johnson has scored two goals in his last three games. Each has shown that all these years later, they still have the instincts that made them such prized prospects when they first played in MLS.

Now we have come to the present, and the day on which Adu and Johnson will finally be reunited. So here are the answers to the trivia questions that soccer fans across America will be asking this weekend:

March 28, 2010 was the last time that Adu and Johnson played in the same game, as teammates for Aris Thessaloniki.

June 4, 2008 was the last time that Adu and Johnson were on the field together for the U.S. national team, a 1-0 loss to Spain in Santander.

It has happened a total of three times. The other two were a 2-0 loss to England at Wembley Stadium on May 28, 2008; and a scoreless tie against Canada at San Diego's Torero Stadium on January 22, 2006.

August 24, 2005 was the last time that Adu and Johnson played against each other as players in Major League Soccer.

The game was a U.S. Open Cup quarterfinal between D.C. United and FC Dallas at the Maryland SoccerPlex in Boyds, Md. Dallas won it on penalty kicks, 4-1, after extra time finished with the score 1-1.

September 11, 2004 was the last time that Adu and Johnson played against each other in a Major League Soccer game. It was a 3-0 win by D.C. over the Dallas Burn at RFK Stadium.

Johnson started, and Adu came on a substitute in the 71st minute. Adu scored the third goal, in the 84th minute. Current Union youth technical director Alecko Eskandarian scored the other two (and suffered a concussion as well).

Adu and Johnson also played at the same time in both of the other games between United and the Burn that year. The first was a 1-1 draw at the Cotton Bowl on June 26, and the second was a 5-1 Dallas win at the Cotton Bowl on July 24. Johnson scored twice in the latter contest.

So why have I dragged you through nearly 1,500 words of rambling today? For two reasons.

The first is simple. I think both Johnson and Adu are capable of getting back to the U.S. national team if they continue to play well in MLS.

The second is more complicated. MLS clubs have put a lot of time and money into improving the quality of their international signings in recent years. That has been manifest in a lot of ways, from David Beckham to Roger Torres to Seattle star Mauro Rosales.

But for most of its history, the core function of MLS has been developing American talent. The list of such names is long: Clint Dempsey, Tim Howard, Jozy Altidore and so many others.

In the last couple of years, that pipeline has shown signs of starting to dry up.

Outside of Juan Agudelo, MLS has not produced much top-quality American attacking talent lately, and you can argue that the Red Bulls have restricted Agudelo's growth as much as they have helped it.

At the other end of the field, none of MLS' young goalkeepers has yet shown the ability to follow in Howard's footsteps - as evidenced by the struggles of D.C.'s Bill Hamid and Chicago's Sean Johnson at the CONCACAF Olympic qualifying tournament.

Concurrent with this is the fact that a number of MLS clubs place a higher value on short-term success than long-term development. There's nothing inherently wrong with this, of course, but there's a significant contrast between how Seattle and Philadelphia have built their respective rosters.

The Sounders' squad has 14 Americans and no home-grown players. The Union's squad has 19 Americans - 20 if you count Danny Mwanga - and three home-grown players. That's a very big difference.

Seattle's enormous fan base can rightly point to the fact that their team has made the playoffs every year of its existence in MLS, has won three straight U.S. Open Cups, and has done well in the CONCACAF Champions League.

In addition to this, there are a lot of people in Seattle who feel scorned over the fact that the U.S. Soccer Federation refuses to play men's national team games there.

The result, from what I've seen when I've been in Seattle, is that some good friends of mine who are pretty influential in the Sounders' fan base have decidedly mixed emotions when it comes to attitudes towards developing American talent.

(Right after this blog post went up, @sounderatheart tweeted at me: "If you focus on developing Americans you'll miss the goals." That's an example of what I'm talking about.)

It's not just Seattle, either. The Red Bulls have been criticized in the past for similar sentiments, as I noted above. I've also seen a similar sentiment starting to grow among Canadian fans towards the Vancouver Whitecaps, although they are hampered in part by extra rules on how many Canadian players the Canadian MLS teams can carry.

It may not be a majority of the respective fan bases, but it's clear and it's loud. More importantly, the front offices are sending messages by their signings, and their use or lack thereof of Homegrown Players.

I get that. I understand their annoyance, and what fuels it. But by contrast, I've seen many comments on my blog in the past from Union fans who want to see the team sign and develop American players specifically.

Again, both teams' philosophies have strengths and weaknesses. In the end, a team's trophy case does tend to speak more loudly than other measures of success. The Sounders have won things, and the Union have not.

The clash of philosophies will be on full display on Saturday, but so too will two players who have come a long way to return to the spotlight. Eddie Johnson and Freddy Adu have earned this moment, and it will be fascinating to see how they interact with each other.

So for this week, I'll let the rest of you talk about Mauro Rosales, Fredy Montero, Gabriel Gomez and Lionard Pajoy. I'll be focusing my attention on two American stars, playing a showcase game in America's league.

I think that matters, and I have a hunch that I'm not alone.