Short Answer 
The liberation of Nazi death camps exposed the extensive scale of mass extermination and systematic brutality, shocking the world. The secrecy and propaganda surrounding the camps contributed to disbelief until their revelations prompted global outrage and condemnation of the atrocities committed.
1. Size and Scale of the Camps
The sheer magnitude of Nazi death camps was one of the primary reasons for global shock. The camps were extensive, with large networks dedicated to the mass extermination of individuals. Survivors’ testimonies illustrated the staggering numbers of victims, emphasizing the systematic approach the Nazis employed to carry out these atrocities.
2. Secrecy and Propaganda
The significant level of secrecy surrounding the camps contributed to the disbelief many had before their liberation. Many people outside of Nazi-occupied areas were unaware of these facilities and the full extent of the brutalities enrolled within. Propaganda often painted a misleading picture which led to skepticism about reports of genocide, making the revelations even more shocking when verified.
3. Global Reaction and Outrage
The combination of discovering the camps’ existence, their large scale, and the covert operations led to a profound global reaction against the Nazi regime. The locations of these camps were often in regions viewed as safe, contributing to the disbelief. As more details became public, the global outrage grew, uniting people in condemnation of the horrors witnessed.