Toward the end of World War II in 1944, Allied forces advanced from the west, while forces of the Soviet Union advanced from the east. Trapped in the middle, the SS – not wanting the world to know about the Holocaust – decided to abandon the Nazi concentration camps, moving or destroying evidence of the atrocities they had committed there. Thousands of prisoners were killed in the camps before the marches commenced. These executions were deemed crimes against humanity during the Nuremberg trials.