Answer:
Vermont is the first colony to ban slavery.
Step-by-step explanation:
Vermont liked to be independent and took the chance to show it was independent on July 2nd of 1777. An abolitionist called to ban slavery, which Vermont responded by abolishing slavery outright first. Not only did Vermont's legislature ban slavery, it allowed full voting rights for African-American males. Later in 1858, November 25th, Vermont decided to take it further and ratify a stronger anti-slavery law to its constitution.
That's on period :)