An underused trope is Civil War interventionism not where it involved the French and/or British joining on the side of the Confederacy, but the fact that Russia had good relations with the United States and would have joined the war on their side had the British and French gotten involved. And therein lies the issue of various alliances and friendships which have the grave potential to make life interesting, in the Chinese sense. And the potential for a global conflict. I do think it had the potential, though not necessarily the destiny, to become a world war. It would have been a larger conflict regardless.
So what if, in reaction to British and/or French intervention, the Russians intervened?