During the era of slavery in the United States, the education of African Americans, enslaved and free, was often discouraged, except for religious instruction, and eventually made illegal in many of the Southern states. It was believed that literacy was a threat to the institution of slavery. First, literacy facilitated knowledge about the successful slave revolution in Haiti of 1791–1804, the end of slavery in the British Empire in 1833, and the writings of abolitionists. Secondly, literacy allowed or potentially allowed slaves better access to information about the Underground Railroad and other routes to freedom.