So beyond the obvious parallel of slavers vs non-slavers, there seem to be loads of parallels between the popular memory of the US civil war and the main conflict of F:NV.

The NCR are the US, nominally about freedom but with major limitations and a nasty territorial streak. Their soldiers are less well-trained, but better provisioned and in the hands of talented leaders like Hsu, they can be decisive.

The Legion would be the CSA, poorly equipped, only existing on what they can plunder, but with a reputation for bravery among their rank-and-file, and a few talented leaders who formerly were citizens of their opponents. They also have a fan base of edgy basement-dwellers who idolise their culture despite its brutality.

I suppose the Khans would be Native American groups, and House would be New York: nominally on the Union side.

There are limitations of course. Hsu may be Sam Grant, but Kimball is no Lincoln.