If you want to play that game, then the US was not legitimate since only White Male Landowners over 21 could vote at the time of its founding. It was many many years before a majority of the adult residents could vote....well into the 20th century. Something tells me you would not find the United States illegitimate until about 1919 or so.
IMO, the South was improved by Northern conquest. The US has been in a constant struggle to improve itself... and has often failed, but has made progress at times... But back to the question I asked you; are you going to answer it?