Final answer:
Mandelbaum was freed due to the liberation of Nazi concentration camps by Allied forces as they advanced through Europe, with the Soviet army liberating Auschwitz and other camps being freed by American and British soldiers.
Step-by-step explanation:
Mandelbaum regained his freedom as a result of the advances made by the Allied forces during the final months of World War II. As the Soviet army moved from the east and the western Allies from the west, the Nazi concentration camps were liberated.
Specifically, Soviet troops liberated Auschwitz in January 1945, uncovering the atrocities within, including the gas chambers and surviving prisoners.
In the following months, the Western Allies, composed mainly of British and American units, liberated additional camps such as Buchenwald, Bergen-Belsen, and Dachau. The horrors they discovered were widely reported, bringing global attention to the Holocaust.