Germany and Poland.
Unfortunately, there were dozens upon dozens of death camps, or concentration camps as the Nazis preferred to call them. However, they were all centered in Germany and Poland. Poland was primarily where the camps were because that was basically 'Jew central'. It was also the first country in the war to be invaded and conquered.
The extermination camps were in Poland: Auschwitz-Birkenau, Belzec, Chelmno, Majdanek, Sobibor, and Treblinka. The major concentration camps were mainly in Germany, although Stutthof was in Poland. The Major camps in Germany were Buchenwald, Flossenburg, Nathausen, Neuengamme, Ravensbruck and Sachsenhausen. Altogether there were roughly 15,000 camps in Nazi-occupied Europe. Please see the following link for a source of information about the lesser-known Nazi camps.
Concentration camps :)
no one prevented the Holocaust, it happened.
Germany and Poland.
germany ____ No, actually in German-occupied Poland.
The death camps were located in Poland and Germany.
The largest death camps were in Poland. Germany had death camps also but on a lessor scale. The Germans were responsible for all of them.
the Jews were killed at death camps mainly in Poland and Germany by the Nazis
The extermination camps were all in Poland after Germany invaded them. The main extermination camp was the Auschwitz-Birkenau death camp near Krakow, Poland.
Unfortunately, there were dozens upon dozens of death camps, or concentration camps as the Nazis preferred to call them. However, they were all centered in Germany and Poland. Poland was primarily where the camps were because that was basically 'Jew central'. It was also the first country in the war to be invaded and conquered.
Poland
The death camps were kept outside of Germany because even if the people held there managed to escape somehow, they would have so far to go if they wanted to get back to Germany. As well, the supplies locally outside of Germany were cheaper to help build the camps.
The extermination camps were located in Poland, including areas annexed from Poland during World War 2. There was also one near Minsk, Belarus.Please see the related question.
The main concentration camps in Germany proper were Esterwegen, Neuengamme, Bergen-Belsen, Ravensbruck, Sachsenhausen, Mittelbau-Dora, Buchenwald, Flossenburg, Dachau, and Grafeneck. Note that while many, many deaths occurred in those camps, they were not built specifically as death camps (except for Grafeneck) - most of the death camps were in Eastern Europe, especially Poland and Czechoslovakia.
WWII began when Adolf Hitler decided to dominate Europe. The war started when Germany attacked Poland. Other nations joined the war after Germany decided to create an Aryan race and opened death camps for their enemies and Jewish people.