I would propose that the presence of a lawfully-organized Civil government implied the existence of a nation, yet it was a nation which did not receive full recognition by foreign nations, which would have elevated it to equal status in the Law of Nations.
Aside from that, though, your proposition is absolutely, 100% true, as the South was fighting a war for its independence, and lost. As a result, we remain mere vassals of the Federal power, subject to its sovereignty in no less manner than the serfs of old. I'd hardly hold that up as a shining example of American governance, but I'll gladly admit the reality of the situation.
Regards,
~dt~