During 1939 and 1945, the Nazis invaded and occupied lands across Europe and were able to establish more than 20,000 camps. Concentration camps were used to hold prisoners. Camps were divided into sections, and were each separated by rows of barbed wire fences. Prisoners were housed in wooden or brick-built barracks, which were meant to hold between 250 to 400 prisoners, but was forced to hold 700 to 1200 prisoners in each. Each of these brick-built barracks would have its own cruel guard or block commander. Prisoners were kept in incredibly harsh conditions, in which they didn’t have any rights.
Concentration camps were initially built to stop opposition and instill terror, and included groups such as communists, socialists and social democrats, Jehovah’s Witnesses, homosexuals, Roma, and ‘asocials’. However, after March 1938, when the Germans added Austria into German territory, they detained thousands of German Jews in Dachau, Buchenwald and Sachsenhausen concentration camps. Local makeshift internment centres were usually located in or around cities. However this system did not work, and more purpose-built camps were needed. The old camps were later replaced by centrally organised concentration camps under the control of the SS. By 1939 there were seven major concentration camps established by the Nazis. They each housed thousands of alleged political opponents, but later on the Nazis used these centres for the imprisonment of thousands of German Jews, homosexuals and ‘anti-socials’, rather than the political prisoners they were once used for.
In order to keep everything organized they made a camp system. This was a major tool in which the Nazis would assert terror and control over local and national populations. The camp system included forced labour or work camps, death camps, concentration camps, and transit camps. The Nazis used this camp system in order to promote and carry out their anti-Jewish policies across the entire content of Europe.
The Final Solution
The ’Final solution’ was a code name for the murder of all the Jews in Europe. They used this name to make the act itself seem less cruel. It’s not exactly known when this plan was implemented by the leader of Nazi Germany. Before, Nazis just sponsored programs that basically aimed to isolate Jews from society and drive them out of the country, but later decided to just murder them. With that, the Jews were usually ordered to gather within close proximity of railroad stations. They were then deported to the extermination camps on long, grueling trips under terrible conditions. These rides were able to kill some passengers before they even got to the death camps. When The Jews of Europe got to the death camps they were then systematically murdered as part of the Final Solution. 
Hamda Adan
The Holocaust - A Visual History 