According to the Feds, it was always part of the same country, and could not secede. And after the war, it is obviously the same country.
The people who actually fought the war were wiser. They worked together to acknowledge the worth of many who fought - south and north - and allowed the worthy to be honored. (Who can honestly assert that R.E. Lee and T. J. Jackson were not good and noble men?)
Good point. The official position of the United States of America has always been that the Confederacy was never a separate country.