"The Americans with Disabilities Act was passed by Congress in 1990. It was amended by Congress in 2008 [An amendment that broadened definitions of disability, expanding protection and services to more people.]. This is the law that protects the civil rights of people with disabilities in many aspects of public life." - ada.gov
Check out this research guide by the Library of Congress, "Disability Law in the United States: A Beginner's Guide," to understand and explore the history and legislation around disability law.
Learn more by listening to ADA Live!, a monthly podcast that explores topics with guests who have "knowledge, experience, and successful strategies that increase the participation of persons with disabilities in communities and businesses." An episode guide can be found here.
For more digging, check out Duke librarian, Ryan Denniston's, research guide on the Legislative Process.