Caesar's Legion spawned from the Grand Canyon area ( Van Buren) migrating west to Nevada. In 2281, Legate Lanius commented that the West would fall as the East fell and that all the land between would bear the mark of Legion. The main story of Fallout: New Vegas takes place in the year 2281. A very limited selection of these mods are available on Xbox and PS4.
This page suggests up to 100 mods that you can install to enrich your New Vegas universe. PC users, it is strongly recommended to use Mod Organizer 2 so that you can configure a profile dedicated to New Vegas, without interrupting your currently installed mods! Do NOT use the inferior Vortex which limits you at the 254 plugin cap with no work around.