Borussia Dortmund burst on to the scene in 2010 when a fairly unknown Jurgen Klopp team came in ahead of Bayer Leverkusen and favourites Bayern Munich to win the Bundesliga title.
The season before they had finished in fifth place and their surge for the title was immense. Led by their ecstatic manager and their, arguably, best players Lucas Barrios and Nuri Sahin, they achieved something nobody was expecting. In the summer of 2011 Sahin left for Real Madrid to look for bigger and better things. This would become a constant theme for Dortmund in the next few years.
In the following season Barrios lost his form but was ably replaced by Lewandowski, who would go on to score 22 league goals. He was supported by Kagawa and Gotze who were magical in their ability to unlock defences and score thrilling counter-attacking goals. Klopp proved to, once again, be a master in finding talent as he promoted Gundogan into the first team as a Sahin replacement.
The German youngster originally found it tough but was soon pulling the strings from his holding midfield role next to Sven Bender. Dortmund went on to better their points tally of the year before and win the double after securing the DFB-Pokal with a memorable 5-2 win over Bayern Munich. However, this came at the cost of a poor Champions League campaign. They were blowing Germany away but Europe still looked at them as something exciting that would dwindle and die soon enough.
The summer of 2012 dealt Klopp and his team another huge blow as Kagawa could not resist the lure of Manchester United. Klopp sold the Japanese forward for £14 million after buying him for £300,000 two years earlier - a masterstroke. This allowed him to buy Reus, who proved a more than capable replacement, and welcome home Nuri Sahin after his unsuccessful spells at Real Madrid and Liverpool. The season of 2012/13 proved to be as mental as BVB fans had come to expect.
They came second in the league and the Champions League and in doing so lit up Europe and put Dortmund firmly on the footballing map. People were watching them and they were getting excited. It is safe to say that, come the latter stages of the tournament, they were every fan's 'second team'. Lewandowski, Gotze, Reus and Gundogan showed their quality and Klopp's celebrations became famous.
However, the annual selling of the club's best players persisted with Mario Gotze doing the very thing that would prove unforgivable and joined Bayern Munich. The money was used to acquire Henrikh Mkhitaryan and Pierre-Emerick Aubameyang, two relatively unknown players who were given the chance to fight for Gotze's vacant position behind Lewandowski.
Dortmund have experienced a lot of success over the last few years and have promoted players and made them into stars. This is the first step to becoming a big European side. The second step is managing to keep hold of the players you promote. This has been difficult for Dortmund and they have relied heavily on Klopp's ability to find excellent replacements but the trend needs to be broken if they are to consistently compete with a very strong Bayern side. With Lewandowski already stating his desire to leave in 2014 and the vultures circling around Hummels, Gundogan and Reus it will be a major challenge to continue replacing them.
They cannot let themselves become a feeder-club for richer and 'bigger' clubs otherwise they run the risk of falling into a lull similar to the one one Arsenal experienced over the last few years. Nasri, Fabregas, Song, Van Persie and Clichy all followed money and the promise of success and trophies. This meant that by the end of last season Arsenal were celebrating a fourth-place finish like a trophy whilst Van Persie was celebrating taking the Premier League title off Nasri and Clichy.
Dortmund have the means to become great but the key is keeping their stars and - if they must be sold - then not to a direct rival like Bayern Munich. If Dortmund can overcome this barrier and become more desirable to their players than the clubs trying to lure them away, then they have truly broken the barrier and can be considered a top European side.
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