Concentration camps were different from death camps. Some of the more infamous concentration camps were Buchenwald, Bergen-Belsen, Dachau, and Ravensbrück. These were prison camps which the Nazis set up before World War II started. The Nazis sent people who they did not want in their society to these concentration camps. The Nazis forced millions of people to do forced labor in the concentration camps. Prisoners in concentration camps made up about 25% of the workers in Nazi Germany. Even though the concentration camps were not designed for mass murder, over 75% of the people sent to these camps died because of starvation, illness, exhaustion, executions, and physical abuse.
In the early years of World War II, the Jews were mostly sent to concentration camps. However, from 1942 onward, they were mostly deported to the death camps. They were told they were being "resettled" - sent to other places to live. The Nazis built many of the death camps in Poland, which the Nazis controlled. They did this because most of the people they wanted to kill lived in Poland. Poland had the most Jewish people in the parts of Europe that the Nazis controlled. Also, since these death camps were not in Germany, the Nazis could hide what they were doing from the German people.
The Nazis created two types of death camps. Some were "pure extermination camps." Their only purpose was to kill people. Others were a combination of concentration camps and death camps. At these camps, the Nazis would kill some people right away. They would force others to work as slaves until they died.
The first death camps were Treblinka, Bełżec, and Sobibór. They were built during Operation Reinhard (October 1941 – November 1943), whose goal was to kill all of Poland's Jews. Trains full of people were sent to these camps, and were murdered as soon as they got there. At first, the camp's guards used carbon monoxide to kill the prisoners. They then buried their bodies in mass graves. Later, when there were too many bodies to bury, they started burning the bodies. So they could kill people and get rid of their bodies more quickly, the Nazis built gas chambers and crematoria in Treblinka and Bełżec. At Bełżec, they also started using Zyklon-B poison gas to kill people.
On December 8, 1941, the Nazis opened another death camp called Chełmno. At first, they killed prisoners at Chelmno inside vans, using carbon monoxide exhaust fumes. Later, like at the other death camps, the Nazis built gas chambers so they could kill more people at a time. Almost all of the prisoners sent to Chelmno were killed right away. However, the Nazis forced a few strong men into work units called "Sonderkommando". These prisoners were forced to help take dead bodies out of the gas chambers and burn them.
The death camps were small (only several hundred meters long and wide). They also had very little housing or other buildings. Because of this, the Nazis were able to trick the prisoners when they arrived. The Nazis told them they would only be staying at the camp for a short time, before continuing to a work camp farther east. This kept the prisoners from panicking or fighting back.
After they decided to start the "Final Solution," the Nazis built gas chambers and crematoria inside some of the concentration camps that already existed, like Auschwitz and Majdanek.
When people arrived at these camps, they would go through a process called "selection." Nazi guards would choose which prisoners would be kept to work as slaves, and which would be sent right to the gas chambers to be killed. Usually, the Nazis sent elderly people, sick people, and very young children right to the gas chambers. Healthy people were often kept for slave labor, and were forced to work until they were too sick or starved to work as fast as the Nazis wanted. Then the Nazis would "select" them for the gas chambers.
With the support of Nazi Germany and fascist Italy, the Independent State of Croatia (ISC) was created on 10 April 1941. It was ruled by the fascist Ustaše government, which agreed with the Nazis' ideas about race and politics. The Ustaše agreed with the idea that all Jews and Roma people should be killed. They also agreed with the Nazis that socialists and communists were political enemies.
The Ustaše built death camps in the Independent State of Croatia and helped with the Nazis' "Final Solution" by killing many Jews and Roma. However, their main goal was to kill all of the Serbian people in the ISC. The Ustaše treated the Serbian people so cruelly that even the Germans were shocked.
The first Ustaše camp was Jadovno concentration camp. It held thousands of Serbs and Jews from May to August 1941. Prisoners were usually killed by being pushed into deep ravines near the camp.
The Jasenovac concentration camp replaced Jadovno. Jasenovac was a very large group of many camps. Many prisoners who arrived at Jasenovac were immediately scheduled to be killed. Strong men who could work, and were sentenced to less than three years in the camp, were allowed to live. However, all prisoners sentenced to three years or more were immediately scheduled for execution.
Some prisoners at Jasenovac were killed with poison gas or in mass shootings. However, the Ustaše guards killed many prisoners using their hands, or tools like knives and hammers.
In 1941, top Nazi official Heinrich Himmler went to see a group of "Einsatzgruppen" perform a mass shooting. The group's commanding officer told him that shooting so many people was psychologically harming the soldiers doing the shootings. Himmler decided the Nazis needed to find another way of killing people. After the war, the diary of Auschwitz's Commandant, Rudolf Höss, showed that many "Einsatzkommandos" – the killers – either went mad or killed themselves. He wrote that they did this because they were psychologically "unable to endure wading through blood any longer."
The Nazis had learned from their T-4 program that they could kill people using carbon monoxide. However, they thought sending carbon monoxide to the death camps would be too expensive.
In August 1941, Höss' deputy, Karl Fritzsch, tested out an idea. At Auschwitz, clothes infected with lice were treated with crystals of prussic acid (hydrogen cyanide). The crystals' brand name was Zyklon-B. They were made to order by the IG Farben chemicals company. Once their container was opened, the Zyklon-B crystals in the air released a deadly cyanide gas. Fritzch thought this gas could be used to kill prisoners. To try out the effects, he locked some Soviet prisoners of war in the basement of a bunker and gassed them. They died.
Gassing with Zyklon-B became Auschwitz's way to exterminate people. It would also be used at Majdanek and other camps. Besides gassing, the camp guards continued to kill prisoners through mass shootings, starvation, torture, and abuse.
During the war, Nazi official Kurt Gerstein told a Swedish diplomat about life in a death camp. On 19 August 1942, Gerstein arrived at Bełżec extermination camp, which had carbon monoxide gas chamber. At the time 45 railroad cars, filled with 6,700 Jews, were being unloaded. Many of the Jews had died on the trip. The rest were marched naked to the gas chambers. There Gerstein said: