American Civil War

   Border Southern states that permitted slavery but did not secede (both KY and MO had dual competing Confederate and Unionist governments)
   Union territories that permitted slavery (claimed by Confederacy) at the start of the war, but where slavery was outlawed by the U.S. in 1862

When Virginia declared its secession in April 1861, Robert E. Lee chose to follow his home state, despite his desire for the country to remain intact and an offer of a senior Union command.

  Gradual emancipation in New York (starting 1799, completed 1827) and New Jersey (starting 1804, completed by Thirteenth Amendment, 1865)
  Effective abolition of slavery by Mexican or joint US/British authority
  Territory incorporated into the US after the passage of the Thirteenth Amendment
In 1863, the Union army accepted Freedmen. Seen here are Black and White teen-aged soldiers.