Nazi Germany maintained concentration camps (in German Konzentrationslager, or KZ) throughout the territories it controlled

The first Nazi Concentration Camps  were hastily erected in Germany  in February 1933 immediately after Hitler became Chancellor and his NSDAP was given control over the police through Reich Interior Minister W Frick and Prussian Acting Interior Minister H Goring .

The first camp in Germany,Dachau was founded in March 1933.

The camps held around 45,000 prisoners by 1933 and were greatly expanded after the Reichstag Fire of that year.

In 1934-35 H Himmler's SS took control of the police and concentration camps throughout Germany and Hitler allowed Himmler to start using the camps' facilities and personnel to purge German society of so-called "racially undesirable elements" like Jews, criminals, homosexuals, and gypsies.

Between 1939 and 1942 during World War II, the number of camps exploded to 300+, as political prisoners and "undesirable elements" from across Europe were mass-incarcerated generally without judicial process.

Between 1933 and the fall of Nazi Germany in 1945, more than 3.5 million Germans were forced to spend time in concentration camps and prisons for political reasons, and approximately 77,000 Germans were executed for one or another form of resistance by Special Courts,Courts- Martial and the civil justice system

Concentration camps became places where millions of ordinary people were enslaved as part of the war effort, often starved, tortured and killed after  Sep 1939 with the beginning of WW II

Types of Camps

1)Hostage Camps

2)Labour Camps

3)Prisoners of War(POW) Camps 

4)Camps for rehabilitation and re-education of Poles

5)Transit and Collection Camps