Google has 950,000/1,100,000 results, that's far from universally. 'US Civil War' is unambigious and thus better; nobody will get lost because of redirection. --
Yooden
I rewrote the first paragraph to give the actual name of the Confederate States of America. "The Confederacy" is as much a nickname as "the Union" was. --
MichaelTinkler, semireconstructed and spatially-displaced-in-Upstate-NY Southerner