[Potowmack]

This was not a civil war, but a war between two separate nations. A civil war is a war between opposing factions fought within the same national borders.

That begs the question: What is a nation?

One of the crucial tests, IMO, is whether a "nation" is recognized by other nations.

AFAIK, Except for a few minor German principalities and, arguably, the Vatican, the CSA was never recognized as a sovereign nation.

[Wallace T.]

One of the German principalities that recognized the Confederacy was Saxe-Coburg-Gotha, where Prince Albert, consort of Queen Victoria of England, was born and raised. The German principality may have been a "stalking horse" for England, which, along with France, toyed with recognizing Southern independence. The Battle of Antietam, which thwarted the first major Confederate attempt to invade Maryland and Pennsylvania, and the Emancipation Proclamation, which provided an ideological appeal to what had been viewed as a mere war of secession, like those of Eritrea in the 1980s or Croatia in the 1990s, tipped the scales in favor of the North. Thereafter, England and France ceased considering active support for Southern independence.