History of Law

https://online.law.tulane.edu/articles/history-of-law-the-fourteenth-amendment
“Some southern states began actively passing laws that restricted the rights of former slaves after the Civil War, and Congress responded with the 14th Amendment, designed to place limits on states' power as well as protect civil rights. To be readmitted to the Union after the Civil War, southern states had to ratify the 14th Amendment.”

After the southern states lost the civil war and the 13th amendment was ratified, the southern states were creating laws that limited the rights of their negro inhabitants who were freed, but had no standing against their state. In response to this Congress proposed the 14th amendment and, in order for the southern states to be allowed back into the union, they had to ratify it as well.