What outside factor most directly contributed to the formation of enclaves in cities

The correct answer is Housing discrimination

Housing discrimination takes many forms:

A real estate agent shows you apartments in one neighborhood and not another because of your race.

An owner refuses to rent to you due to your Section 8 voucher

An owner makes an inappropriate comment about their gender, ethnicity, religion or disability.

You have small children and the owner says he can't rent it for you because the apartment has lead paint.

b, the anti immigrant fervor

the real answer is b