In the early 1900s, native-born Americans, usually Protestants, did NOT consider Irish, Italian, or Jewish immigrants to be white. What does this illustrate?

Explanation:

Race is a social construct, it is not biological. There are no genes common to all whites and blacks so race cannot be genetically verified and it were true then the classification of people based on race would have been constant across boundaries, but it is not so because a person who is categorised as black in US might be considered white in Latin american countries.

The Greeks, Poles, Italian and Hungarian migrants were not considered to be whites in 1800s and 1900s, they tried to overcome it by showing through behaviour that they were worthy of being called white. The people form Netherlands,Ireland,Scandinavian countries and Germany were considered to be white.  

The Americans were afraid that the foreigners would bring peculiar religious practices and substandard ways of living and religious practises to this country , that would bring down this civilisation.

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