Where did the Nazis originally plan to send the Jews before they instead starting killing them in concentration camps?

Explanation

Nazi Germany started executing physically and mentally disabled people in 1939 and managed to kill some 70,000 altogether during World War II. In 1942 the systematic killing of Jews commenced. Before that, it had mainly been persecution and the erection of ghettos. The original idea was to ship the imprisoned Jews to Madagascar, but instead, some 3 million Jews were killed inside concentration camps in the years to come, alongside an unaccounted number outside the camps.