Stalin died in 1953 and is replaced by Khrushchev. Khrushchev was the leader of the soviet union for part of the Cold War. He built the Berlin Wall to keep people in and away from the non-communist side of Berlin and prevent movement.
We kind of laugh now at how ridiculous it is to think a desk could protect you from an atomic bomb. but it must have been terrifying to be a small child in school and being constantly reminded of the threat!