In 2006, the Pittsburgh Steelers became the first sixth-seeded team — the lowest possible seed in the NFL playoffs — to not only make it to, but win the Super Bowl. The Green Bay Packers accomplished the same feat in 2011, three years after the New York Giants won the Lombardi Trophy as a number five seed.

Those unexpected runs are hardly the exception anymore. Indeed, lower seeds are now routinely advancing deep into the playoffs. Where in years past, top-seeded teams dominated the postseason, the past decade has seen a surge of upstarts crash the party.

This phenomenon coincides with a tweak the NFL made in the early aughts to the way playoff teams are determined. And though the change itself seemed fairly minor at the time, it's had a significant impact on the way the postseason has played out since.

For the 1990-91 season, the NFL expanded the playoffs to 12 teams, with six squads representing each conference — the winners of each conference's three divisions, plus the next three teams in each conference with the best records. Over the next 11 years, seven number one seeds won the Super Bowl. Of the 22 teams to make the Super Bowl during that span, all but four were seeded either number one or two. Teams that dominated the regular season also dominated the playoffs.

Then in 2002, things changed. The league expanded each conference from three divisions to four to accommodate the expansion Houston Texans. In doing so, the NFL altered the playoff landscape, with four division winners now earning automatic bids, and the remaining two berths going to the next best teams in each conference.  This change has led to jumbled playoff matchups and more unpredictable results.

How? For one thing, the change diminished inter-divisional competition, providing weaker teams with an easier path to the postseason. Whereas divisions used to include five or six teams apiece, they all now have just four. Fewer teams per division means there's now a greater chance that every team in a division will be lousy. As a result, teams like the 2010 Seattle Seahawks, who finished the season with a losing record, can still make the playoffs by simply being the best of four subpar teams.

On the other side of the coin, the shrunken wild card pool has led to tougher competition for the final postseason spots. A five or six seed can now easily be, in terms of winning percentage, significantly better than their seeding indicates.

Combined, these changes have fostered playoff pools with strong teams on the high and low ends, and weaker division champs in a squishy middle. Oftentimes, this has led to wild card teams taking on higher seeds with worse regular season records. For instance, just this year, the Seattle Seahawks (11-5) — playing in perhaps the best division in football — managed only a wild card and number five seed, while the Washington Redskins squeaked out a 10-6 record to win the surprisingly weak NFC East, scoring a number four seed. The Seahawks were the lower seed and still favored to win the game — despite the fact that it was played in Washington. And win the Seahawks did.

Perhaps more egregiously, consider 2008, when the Indianapolis Colts finished the year at an impressive 12-4, but slipped to the AFC's fifth seed because they did not win their division. That record would have put them in a three-way tie for the NFC's top seed. Nevertheless, they had to travel to San Diego for their first-round matchup with the fourth-seeded Chargers, who ended the season at 8-8 in a division where no team cracked .500.

Returning to the 2005-06 Steelers, their Super Bowl victory is less surprising when you consider their record. At 11-5, they actually tied for the fourth-best record in the AFC. However, the Cincinnati Bengals held the tiebreaker over the Steelers for the division crown, dropping the Steelers into the wild card pool and, ultimately, the lowest seed.

Similarly, the sixth-seeded Packers of 2010-11 technically tied for the conference's fourth-best record at 10-6, but lost their division and wound up as a six seed — behind that infamous 7-9 Seattle team, no less. As for the 2007 Super Bowl-winning Giants, they claimed the fifth seed with the conference's third-best record.

Remember, in the first 11 years of the 12-team playoff format, seven number one seeds and two number twos won the Super Bowl. Since the divisional dilution in 2002, only two top-seeded teams have won the Super Bowl, while the number of lower seeds to win — and to even just reach — the Super Bowl has risen dramatically. Including this year's Ravens, a team seeded fourth or lower has made the Super Bowl in six of the last eight years.

Certainly, the NFL's win-or-go-home playoff format has played a role in this unpredictable pattern of Super Bowl champs. But the move to four divisions, and the resulting effect on the postseason landscape, has only added to the seemingly random list of Super Bowl winners and losers in the last decade.