Complex sentence: It was originally intended to replace both Schönefeld and Berlin Tegel Airport, and to become the single commercial airport serving Berlin and the surrounding state of Brandenburg, an area with a combined 6 million inhabitants.
Split into simpler sentences: It was originally intended to replace both Schönefeld and Berlin Tegel Airport and become the single commercial airport serving Berlin and the surrounding state of Brandenburg. This is an area with a combined 6 million inhabitants.