In the 1800s, what was the most important motivation for both "old" and "new" immigrants to settle in ethnic neighborhoods?

The answer is common language. It could also be common culture since they are all from the ethnic race, it promotes a sense of community where people feel safe knowing that they are among their fellow countrymen in a new land.

Answer;

C. a common language.

In the 1800s, an important motivation for both "old" and "new" immigrants to settle in ethnic neighborhoods was a common language.

Explanation;

The old immigrants came from the northern or western Europe while the new immigrants came from southern or eastern Europe.

Old immigrants were protestant while the new immigrants were Catholic, Orthodox or Jewish.