Yep, their rise is a mirror of that of America. Which is why the likes of Caesar and House tell the player that the NCR is doomed to the same failings as pre-war America and it would just be history repeating itself with the NCR. I would say that in the timeline of New Vegas that the NCR is more or less in the same camp as America was during the Oregon Trail days. People are moving out East now instead of West, the Republic is looking to expand in order to support their growing population, the NCR is starting to get into conflicts with tribes out East over land. Pretty much a mirror of America during the days of the Oregon Trail.