Question

Which part of the U.S. Constitution was added after ratification to address the concerns of the Anti-Federalists?

Answer 1

I think the answer is: Article of Confederation
The anti-federalist strongly oppose the formation of a stronger government and ratification of the Constitution.
In order to address the issues, it is stated in the article of Confederation that there will be a separation of power in the government in order to make the government become weaker.