What was the rationale behind Plessy v. Ferguson decision of 1896?

Plessy v. Ferguson, 163 U.S. 537 (1896), was a landmark decision of the U.S. Supreme Court that 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".

b - those executed came from every social and economic class

the answer to your question is

the treaty of hopewell