Original: The Waffen-SS, the combat branch of the SS (the Nazi Party's paramilitary organization), became the de facto fourth branch of the Wehrmacht, as it expanded from three regiments to 38 divisions by 1945.
Simplified: When East Germany (the German Democratic Republic) was incorporated into "West Germany" (the Federal Republic of Germany) in 1990, much of the Volksarmee property and some of the staff were also incorporated into the Bundeswehr.