This is something I'm confused on. If you choose to launch the missiles at the NCR, Legion, or both, is only one location for each faction (the Long 15 or Dry Wells) nuked? Or do missiles also destroy cities in those nations? I've only played LR once so far, as an NCR character. If you tell Ulysses he doesn't have enough missiles to destroy the West, he says he will turn the Long 15 into "miles of fire" to "cut the bear's throat." But the ending slide, if you launch at both (I did just to see, before going back and preventing the launch), seems to imply the entire civilizations were wiped out.

When you nuke them both it sounds like the die out eventually. They destroyed communities along with the piece of the long 15 and Dry Wells. Then it seems like everything collapsed on itself after the nukes.

The nukes only strike The Long 15 & Dry Wells if you decide to launch them.

But the Long 15 is the NCR's #1 supply rt. in and out of the Mojave, without that road the NCR stands no chance in securing a hold in the Mojave Wasteland.

As for Dry Wells that was the home of The Twisted Hairs, Ulysses old tribe, though sadly I don't know how important this location is to the Legion or if it is a major supply line for them just as The Long 15 is for the NCR.

By cutting the supply lines you hurt the nation as a whole this is the lesson Ulysses learned from "The Divide" the name of the settlement where your Courier delivered "the package." So he was telling the truth you don't have to send the nukes into NCR territory to hurt them you only have to "cut the bear's throat" by destorying their main supply line in this case The Long 15.

Hope this all helps answer your question, I wish I knew more about The Legion and how important Dry Wells is to their supply lines, if even at all.