Sure you can. Berlin had no chance to really grow all through the Cold War, even worse, part of it was walled off and frontline at the same time. That’s why Berlin’s population plummeted even when Germany’s population grew.
It’s not easy to rebound from that (after 45 years), even when you become capital, pretty much all of Germany’s successful post-war industry established itself in western West Germany. And not just industry, Post and Telekom are both still in Bonn and will probably be forever.
Berlin is also in the middle of a huge sparsely populated area. If there are no companies in Berlin that have jobs to offer not many people are going to move there.
(By the way, looking at lists with the biggest German cities is a bit misleading. Sure, Berlin handily comes out top, but look at this map: [+]. That’s not a zillion different cities like those silly natives with their tradition would want to make you believe, that’s just one city with five million people in it.)
