Answer:
Nazi Germany built concentration camps in Poland to relocate Jewish people in there, violating their freedom and forcing them to work, killing aproximatly half of them, reaching an estimated number of 6 million Jewish deaths.
During World War II, Nazi extermination centers were built at a later stage of the annihilation program. Usually, the bodies of the victims were cremated or buried in common graves. It has been estimated that some 25,000 extermination and concentration camps were established in the countries occupied by Germany, not including the small camps created ad hoc for the local population.