Heinrich Himmler was the creator of the "Final Solution to the Jewish Problem". The first concentration camps in Germany were built in 1933, initially to detain political opponents. During the war, the camp population expanded and they were used to imprison and exterminate Jews, resistance fighters, and others. The most notorious camp was Auschwitz-Birkenau, where over 1 million people were killed, most of them Jews. Prisoners faced brutal treatment, human medical experimentation, starvation, and punishments. Allies were informed of the atrocities but did not take action until late in the war. After the war, some attempted to deny or shift responsibility for the concentration camps.