There were several reasons why conditions for African Americans became harsher as the nineteenth century progressed.
First, an important reason was the fact that, during this time period, the divisions between the North and the South intensified. As a result, Southerners became more interested in protecting the "tradition" of slavery. This led to the passage of harsher laws, such as the Fugitive Slave Act of 1850.
Moreover, as time passed, the ideas of freedom and equality of the Revolutionary War faded, which meant that less states were willing to voluntarily end slavery or improve the conditions of enslaved people.
Finally, as the century progressed, white men were able to gain more rights and more freedom, generally improving their situation and that of the country. However, as slaves remained the same, the distance between the rights and lifestyle of both groups became even larger.
