German children born in the 1920s and 1930s became adults during the Cold War years. Since membership was compulsory after 1936, it was neither surprising nor uncommon that many senior leaders of both West and East Germany had been members of the Hitler Youth. Little effort was made to blacklist political figures who had been members, since many had little choice in the matter. These German post-war leaders were nonetheless once part of an important institutional element of Nazi Germany. Historian Gerhard Rempel opined that Nazi Germany itself was impossible to conceive without the Hitler Youth, as their members constituted the "social, political, and military resiliency of the Third Reich" and were part of "the incubator that maintained the political system by replenishing the ranks of the dominant party and preventing the growth of mass opposition." Rempel also reports that a large percentage of the boys who served in the HJ slowly came to the realization that "they had worked and slaved for a criminal cause", which they carried for a lifetime. Some of them recalled a "loss of freedom" and claimed that their time in the HJ "had robbed them of a normal childhood." Historian Michael Kater relates how many who once served in the HJ were silent until older age when they became grandparents. While they were eventually able to look back at their place in "a dictatorship which oppressed, maimed, and killed millions", he maintains that an honest appraisal should lead them to conclude that their past contributions to the regime had "damaged their own souls."