The supreme court decision in plessy v ferguson affected african americans by

I'm not sure...

But,

It upheld the constitutionality of racial segregation laws for public facilities as long as the segregated facilities were equal in quality – a doctrine that came to be known as "separate but equal".

I guess

1896 Supreme Court decision said that segregation, the separation of races, was legal in US

Decision established idea of "separate but equal" for US race relations

small european communities with shared traditions consolidated into large new states (apex)