The original Constitution nowhere mentioned "slave" or "slavery". In fact, it tries to dodge that issue in a few places, like where states get to include in their population for representation purposes "three fifths of all other Persons."
Everybody else would call it a nation -- it's more than (say) the European Union.
Pure hairsplitting. Reminds me of the lengthy argument I once had on another board about someone who insisted that the UK is not a "crowned republic" or a "monarchical republic".
News to me and to just about every jurist in the business.