How did the Jews deal with such harsh conditions?

The upper middle and higher class fled to another country. Everyone below found a hiding spot or were sent to concentration camps

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Not all upper and middle class fled. Many were rounded up and sent to concentration camps as well. Those that did manage to flee, usually went to other European countries. As the Nazis moved in, they ran out of places to go. Many countries simply refused to allow them to migrate to their countries so they too were rounded up and sent to camps as well.