Answer:
the Emancipation Proclamation,
Step-by-step explanation:
In 1864, President Abraham Lincoln created a legislation that prohibited slavery in United States. This legislation automatically outlawed the Maryland Assembly since it's coming from the federal level.
As a result, African Americans were free from their obligation to serve their owners. That being said, they still received very bad treatments even after gaining the status as free folks. They're treated as second class citizens, not allowed to get jobs, not allowed to vote, etc.