Which of these would have had the greatest effect on late-19th century immigrants coming into the united states?
a) 13th amendment
b) 14th amendment
c) plessy v. ferguson
d) brown v. board of education

It would be the 14th Amendment that would have had the greatest effect on late-19th century immigrants coming into the United States, since this laid the framework for granting citizenship to all people either born or naturalized in the US.