Regarding World War II where and how did Hitler start the concentration camp? What did he expect to gain from this disaster?
The concentration camp was the logical extension of the Nazi approach to what to do with those deemed as enemies of the Reich. The reality is that starting as early as the early 1930s, Hitler and the Nazis had sought to marginalize its opponents, in particular those of Jewish persuasion. This marginalization took place on social, political, and economic levels. Once this was done, members of the Nazi party wanted to continue the process of silence and marginalization with the forced relocation of Jewish people into the "ghettos" in different parts of Poland and other area where the Nazis had firmly established control. The extension of this forced relocation took form in work camps and concentration camps, which were locations removed from the urban centers where those who lived in the ghettos as well as any individual deemed as enemy of the Nazis could be placed. These areas were where the worst of the Nazis were felt and experienced in terms of forced labor and mass extermination. The concentration camp and its accompanying "Final Solution" became the representation of Hitler and Nazis' desire to consolidate power and eliminate those deemed as enemies and adversaries.
The term concentration camp refers to a camp in which people are detained or confined, usually under harsh conditions and without regard to legal norms of arrest and imprisonment that are acceptable in a constitutional democracy.
Adolf Hitler was appointed chancellor in 1933 and the first concentration camps opened up soon after that. Their purpose was to incarcerate anyone whom they thought was an opponent to Nazi policy. These camps were located all over Germany. In 1934, Adolf Hitler authorized Heinrich Himmler to form the concentration camps into a system. Himmler appointed SS Lieutenant General Theodor Eicke as Inspector of Concentration Camps.
People in concentration camps were experimented on, given little or nor food, tortured, and/or forced to work until they died. The goal was to exterminate anyone who was considered a threat to the Nazi regime. They were seen as sub-humans.
Hitler's first major concentration camp was located in the village of Dachau not far from the city of Munich. Unlike other future camps, there was quite a variety of people incarcerated there: Communists, political enemies of the Nazis, violent criminals, homosexuals, Jehovah's Witnesses and some Jews all were herded through the gates of this camp, past words that said "Arbeit Macht Frei" - Work Will Make you Free.
The SS tested different methods of confinement, worker motivation, ration distribution, etc. at Dachau so it would be perfected for future camps.
At first his camps were merely about consolidating his power. Before long, it became his instrument to annihilate the Jewish population, along with communists, Russian POWs and the Roma (Gypsies).