The Jim Crow laws legalized racial segregation and discrimination against African Americans in the United States. This included segregating public schools and facilities, restricting African American voting through poll taxes and literacy tests, and maintaining segregation in public transportation. The Supreme Court upheld the constitutionality of racial segregation under the "separate but equal" doctrine with its 1896 Plessy v. Ferguson decision, allowing Jim Crow laws to spread throughout the Southern states and some Northern states as well.