The question we want to answer about this sterilization is why? The break up of Yugoslavia and ensuing conflict, very similar to today’s conflict in Syria saw an enormous diversity in the trade and manufacture of small arms, going in and going out of the conflict zones as all the various armed groups tried to get ahold of weapons to arm themselves with. Sterilization almost entirely is done to allow plausible deniability to the presence of a country’s small arms in another location. China in particular made entire batches of small arms with dedicated markings such as M21 on SKS’s, complete with actual serial numbers. These were fed into Cambodia, Vietnam, and Laos during the Vietnam War. This is a photograph I took of while in Burma of one such example-
There is some debate if these are war-time or post-war pouches. This is my "take" of the subject. Those that don't have one consider them post-war. Those that have one in their collection claim them to be original 3rd Reich. You can decide, but I will help you a little, if I may be so bold and offer the following info. I bought several of these in Czechoslovakia, before the wall came down. They were still full of original German WWII MG stuff. Some collectors think they are post war Austrian, but these were behind the iron curtain, left there after the war by the Germans. The construction and material are typical German WWII. They are post war marked, as the Czechs used them after the war. It was standard policy to mark German surplus gear for the Czech Army after the war.
In 1955, the Soviets gave East Germany authority over civilian movement in Berlin, passing control to a regime not recognized in the West.  Initially, East Germany granted "visits" to allow its residents access to West Germany. However, following the defection of large numbers of East Germans under this regime, the new East German state legally restricted virtually all travel to the West in 1956.  Soviet East German ambassador Mikhail Pervukhin observed that "the presence in Berlin of an open and essentially uncontrolled border between the socialist and capitalist worlds unwittingly prompts the population to make a comparison between both parts of the city, which unfortunately does not always turn out in favour of Democratic [East] Berlin."