This was when leaders in Germany decided that they were going to murder the specific religious group of Jews. Jews were sent to death camps so they could be killed as a group. They were gassed, overworked, and tested in medical experiments, which killed about 6,000,000 of them, not to mention the undesirables. Undesirables were people who Hitler looked at as a burden, like mentally ill people. Some Jews' friends and family hid them, some countries managing to save most Jews in their population.