The Plessy v. Ferguson case was significant in US history as it established the legal doctrine of separate but equal, which upheld racial segregation. This 1896 Supreme Court ruling sanctioned discrimination, paving the way for Jim Crow laws across the Southern states. The decision legitimized inequalities, effectively disenfranchising African Americans and reinforcing systemic racism. It wasn't until the Brown v. Board of Education ruling in 1954 that the Plessy precedent was overturned, marking a critical turning point in the civil rights movement. The decision highlighted the enduring impact of law on social justice and civil liberties in America.