The Dark Arena by Mario Puzo

Walter Mosca, hardened by the brutality and desecration of three long years of war, returns to the USA a changed man. But he has no sooner arrived than he knows that he must run back to the land of the enemy, to find the woman who accepts the rage and cruelty of the world around her. Back in Germany, where the bitter aftermath of war is everywhere apparent, American cigarettes will buy almost anything. Against this background the love affair between Mosca and his girlfriend Hella moves to a savage climax as vivid and violent as any scene in The Godfather.