For years, Manchester City were known as the little brother of United, watching as the Reds thrived.
For years, Manchester United easily handled their inferior rivals in derbies, as it was simply the case of a league winner facing an average mid-table team.
However, those years are over, as Manchester City has won the English league for the first time in 44 years, marking the end of an era that gave them little to be excited about.
The summer of 2008 marked the beginning of the end of this era, as City were bought by the Abu Dhabi United Group, who have, for a lack of better words, boatloads of money. That summer, they made their first big transfer splash, buying Robinho for a British record transfer fee of ₤32.5 million. Next summer, they made an even bigger splash, gaining the services of stars such as Gareth Barry, Carlos Tevez, Emanuel Adebayor and Joleon Lescott.
At this point, United had just won the title, and their fans were more than pleased with their EPL and Champions League double. However, United fans couldn't help but notice that, after buying a plethora of players, City were on the rise, quickly closing the gap between the familiar foes with their one advantage: money.
Finally, two years after being purchased by the Abu Dhabi United Group, (in the 2009-2010 season), City made their first big step, as their fans were rewarded by a fifth-place EPL finish, narrowly missing out on Champions League qualification. More importantly, they had finished just three places behind United, showing that becoming a world-class team (like United) wasn't too far out of reach.
After adding key players David Silva, Mario Balotelli, Yaya Toure and Aleksandar Kolarov, City improved once again, coming in third place in the 2010-2011 campaign. Whilst United did win their 19th title, they didn't prove to be as dominant, posting many unimpressive results, such as ties against West Bromwich Albion, Birmingham City and Aston Villa, and even a loss against Wolves.
City were rapidly progressing from the mid-table team they were a few years ago, and United were gradually losing some of their power that made them a force throughout world football.
After becoming even deeper in the summer of 2011, adding Sergio Aguero and Samir Nasri, City were officially one of the best teams "player-for-player" in the world. With this, the Blues had a better chance than ever to propel themselves to an EPL championship and enter the territory of upper-echelon teams that United had been in for almost two decades.
They had the chance, and they took it.
City sprinted out of the gate, holding 1st place for most of the year, and going undefeated until December where they lost 2-1 to Chelsea. Despite a late push by United, which included their holding an eight-point lead with just six games to play, the Blues won on the EPL's final Sunday, clinching the title with a dramatic 3-2 comeback win vs. QPR.
Meanwhile, United struggled most of the season, as Old Trafford didn't seem to be the fortress it once was and has the potential to be. Much unlike themselves, United suffered an astonishing 6-1 loss to City, a 3-2 loss against the now-Championship Blackburn, and a vital 4-4 tie to Everton (after leading 4-2 with about 10 minutes left), all at their home ground.
Although they did suffer injuries,most notably that of Nemanja Vidic who missed most of the season, it was apparent United weren't consistently playing their usual majestic football, often forced to scrape out "ugly" wins in disappointing performances. United's decline wasn't nearly as drastic as City's rise, but even with a 2nd place finish, many are now finding it hard to call them a top-five team in the world.
As for City, they have finally entered the elite class of world football, and while they will surely win some EPL titles in the near future, don't expect United to disappear, as they are still a world-class team, just with a little more competition than before.
Now Manchester can boast two world class teams, a newcomer and a veteran in the upper echelon of world football.
As if derby day needed more excitement.