Answer:
Ghettos were primarily an Eastern European phenomenon during the Holocaust because the Nazis' initial plan for the Jews was to deport them to the east. The Nazis had occupied much of Eastern Europe, including Poland, which had a significant Jewish population. The Nazis believed that the Jews posed a threat to their vision of a pure Aryan race, and they wanted to remove the Jewish population from the lands they had conquered.
The Nazis established ghettos in Eastern Europe as a temporary measure to isolate and control the Jewish population before they could be deported to concentration camps or killed. The ghettos were typically established in poor, overcrowded areas of cities, and were often walled off or fenced in to prevent Jews from leaving.
In Germany and other Nazi-controlled areas, there was a more extensive infrastructure of concentration camps and killing centers that were used to systematically murder Jews and other persecuted groups. Therefore, ghettos were not as necessary in these areas, and the Nazis could move more directly to the mass extermination of Jews and other groups.
Overall, the establishment of ghettos was a specific strategy used by the Nazis to control and ultimately eliminate the Jewish population in Eastern Europe. The location and extent of the ghettoization were determined by the Nazis' goals and the conditions on the ground.