Very basically, at the end of World War 2 the Russians had invaded Germany from the east and the other allies (UK, USA, France etc) from the west. As the whole point of war is to gain territory, the allies had to split up Germany between them. After loads of negotiations, Russia got what became East Germany and turned it into a satelite state of Russia. The other allies did have their own zones in what became West Germany. This is why most UK bases are in northern Germany and US ones in SW Germany. The 'western' allies aim was to eventually return W Germany to the german people, but the Russians wanted to keep the East Germans under heel. This started the cold war with all the western allies now waiting for an attack from the Russians via E Germany. If you do a google on 'cold war' you will probably find more info than you can handle! Hope this sort of explains it.