In baseball, one of the best and most sustainable way to build a successful team is through a strong minor league system. The Cardinals have been perhaps one of the best examples of this over the last few years. Prior to the 2013 season, the Cardinals had the top-ranked minor league system in all of baseball, and since then, they have won three straight division titles, in large part due to homegrown players like Matt Carpenter, Kolten Wong, Michael Wacha, Carlos Martinez, and Trevor Rosenthal.

Sometimes, the success of the minor league system overshadows the other factors that go into building successful teams. Since John Mozeliak took over as Cardinals GM, the Cardinals have made several excellent trades that were crucial in building teams capable of reaching the postseason. For example, the 2011 Cardinals were successful because of players like David Freese and Matt Holliday, who Mozeliak acquired in exchange for a fading Jim Edmonds and a package of prospects who never panned out. That year, Mozeliak also made a big move at the deadline, acquiring Edwin Jackson, Octavio Dotel, and Marc Rzepczynski in exchange for Colby Rasmus. While many criticized the Cardinals for trading Rasmus, it is hard to argue against the trade in hindsight, since each of the players the Cardinals acquired contributed in some way to the team's 11th World Series title.

This year's Cardinals team also has key contributors who were acquired via trade. Three trades stand out in particular, with the Cardinals being clear winners in two of them and, at worst, co-winners in a third. (Yes, win-win trades are possible.)

Trade #1: Allen Craig and Joe Kelly for John Lackey and Corey Littrell

This trade is turning out to be one of the most lopsided deals in recent memory, despite the fact that some "experts" were critical of the Cardinals at the time the deal was made. (If you're looking for something funny to read, take a look at this piece from Bob Nightingale in which he called the deal "an absolute heist for the Red Sox.") Not only did the Cardinals get a season and a half of Lackey,including 2015 at close to the league minimum salary, but they also got rid of Allen Craig and his nearly $30 million dollar contract. The only player of value the Cardinals gave up was Joe Kelly, who at the time had accumulated just 2.2 fWAR in 266 major league innings.

The Cardinals have gotten incredible value out of Lackey this season, including a 2.69 ERA, 3.56 FIP, and 3.6 fWAR in 214 innings. While his ERA is unsustainably low due to a ridiculous 83 percent strand rate (his career average is 72.9 percent), Lackey has pitched a high quantity of innings with a FIP that is comfortably above league average. At the league minimum salary, Lackey has been an absolute steal for the Cardinals in 2015, and he may provide further value to the team in the postseason, where he has been quite successful throughout his career.

This trade could also pay dividends down the road if the Cardinals give Lackey a qualifying offer and he leaves in free agency. The Cardinals may even get something out of Corey Littrell, who put up an excellent season at Palm Beach this year (2.69 ERA, 4.43 K/BB in 130 innings).

Trade #2: David Freese and Fernando Salas for Peter Bourjos and Randal Grichuk

At the time this deal was made, Freese and Salas had little value to the Cardinals. Trading Freese opened up a spot for a better player in Kolten Wong (Matt Carpenter moved to third), and Salas was mostly redundant in a bullpen stocked with right-handed pitchers.

Bourjos was supposed to be the centerpiece of the deal for the Cardinals, and he did provide nearly two wins of value to the team in limited playing time last year. However, Grichuk has been a key player for the Cardinals in 2015, filling in admirably in center field and sparking the offense with his barrage of extra base hits. In total, Grichuk has been worth 3.0 fWAR in 341 plate appearances this season. While it is legitimate to question how well he will perform going forward, especially given his high BABIP and bad plate discipline, we can still appreciate the value he has already provided, which is probably more than anyone expected from him when he was first acquired.

Trade #3: Shelby Miller and Tyrell Jenkins for Jason Heyward and Jordan Walden.

Now that the season is nearly over, we can do a much better job of evaluating this trade, at least from the Cardinals' perspective. Heyward has been worth nearly six wins to the Cardinals in 2015 through a combination of above average offense (.292/.358/.439, 120 wRC+) and elite defense (21.6 UZR, 24 DRS). Shelby Miller has had a fine season with the Braves (3.47 FIP, 3.2 fWAR), but he had little value to the Cardinals, especially given their desire to put Carlos Martinez in the rotation.

For 2015, this trade probably couldn't have turned out much better for the Cardinals (excluding the Jordan Walden injury). Heyward put up one of his best seasons yet, and Carlos Martinez had a breakout year after stepping into Shelby Miller's rotation spot, establishing himself as one of the best young pitchers in baseball. Regardless of what happens with Heyward in free agency, I feel comfortable calling this trade a successful one for the Cardinals. Not only did Heyward turn a black hole into a strength (as Joe Schwarz recently pointed out), but he also may have been the difference between the Cardinals winning the NL Central and being a wild card team.

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John Mozeliak is often considered one of the best GMs in baseball, and it is easy to see why, given his track record with trades. Like previous Cardinals teams, the 2015 Cardinals have been successful in large part because of contributions they received from players acquired in trades. With the playoffs set to begin in a few days, here's hoping that these win-now moves pay off in a big way in the coming weeks.