The Legion has no strategic interest in taking the Mojave and in the end it will be impossible for them to hold it or make advances into California.

A. The Tunnelers swarming the Mojave from Lonesome Road will ensure that the human only Legion force garrisoned in the area will not be able to protect the city from being overrun by the creatures. Listen to Uylesses about the threat the tunnelers pose. Any creature that can kill a deathclaw, move underground, is heading towards the Mojave and seeks out humans to kill unlike Deathclaws will break the Legion in the Mojave.

B. The NCR will continue to send missions to the Mojave to kill their leadership. The NCR also has significant military capabilities to disrupt the Legion hold on the area. Talk to Oliver at the end of the game about his intention to continue to harass the Mojave.

C. Just as the Divide kept top NCR forces out of the Mojave and slowed supply lines it will do the same to the Legion trying to advance into California. When you add in the tunnelers and NCR they have no hope of expanding past the Mojave.

D. According to Legate during the end game it took years of resources to start the second battle for the Hoover Dam and yet in most endings in the game (3 out of 4) the Legion loses, even when the player does not kill one Legion solider. The odds are not in Caesars favor for winning and it does not seem the Legion has a large enough force to dislodge the NCR from the Dam, a position they have fortified for 4 years.

E. Vegas is not worth the risk, time or resources Caesar has poured into it. For all of the years of labor, time and effort he has put into conquering Vegas he could of simply built himself a great capital in Flagstaff and expanded his empire in other directions. Vegas has no manufacturing and is basically some [censored] houses and gambling dens. Caesar does not seem interested in using the Hoover Dam for any manufacturing purpose and if it is under Legion rule Vegas would not be a great trade city but one dependent on the rest of the Legion held lands to survive. Talk to Legate with high barter about this matter he will basically agree to the same thing.

A: Do we even know if they'll spread? And how do you know the legion won't be able to beat them?

B: The NCR won't be in a poistion to do anything after getting kicked out of the Mojave.

C: I-15

D: That's Gameplay. The Legion wins when you don't kill any NCR soldiers in the Legion ending?

Because it's the Legion ending.

E: Vegas has Water and Power and People. And even if for whatever reason the Legion doesn't use those resources, they deny the NCR those same resources.

Does the Legion even know about the tunnelers?

I don't think anyone knows about them apart from the Couriers.

The thing about Legion is that even though you can have them win, because it's your game and you make the choices, it's quite plain that in a 'canon' version of events they aren't the intended victors. They play the role of the hyper-authoritarian, utterly terrifying imperialists slowly gaining power over the holders of the region - that's a role made to be defeated. The fact that they're most likely your prime enemies in 3 out of 4 runs is indicative of that. I honestly don't think much thought went into the logistics of Legion controlling the Mojave.

I think that Vegas would be a pretty big trophy and symbolic victory for the Legion. It would also be a stepping stone to pushing farther west. They'd force the NCR out, stomp out local resistance, and fortify the area. Now they've got a nice launch point on the California border, a number of abandoned camps and war materials, fresh water, and a new supply of slaves.

The NCR, already dealing with clueless leaders, corruption, and supply shortages, is going to have a pretty hard time recovering from a defeat in the Mojave (losing troops, land, income from taxes, power from the dam). They may try harassing the Legion borders and such, but I doubt that'd be very effective. The Legion are much better at guerrilla warfare, survival, and raiding.

Once they've fortified and regrouped, they'll start sending Frumentarri and raiding parties up down the I15.

That's what I figured.

How would Caesar know of the potential threat the Tunnelers could be to the Mojave?

Caesar wants to take the Dam because the NCR wants it and if Caesar can take it, he hopes it would badly hurt the NCR in terms of morale and it would deprive the NCR of energy which it needs.

I am pretty sure it is also mentioned that the Legion has yet to come across a city in such good shape as Las Vegas and he hopes to turn it into his Rome (the city) for his Empire.

If you look at a map, if he takes the Mojave, he would be a stones throw away from LA which is pretty much the heart of the NCR.

His over all goal is for the Legion to take everything the NCR has for his own and the Mojave would be a good start and again looking at a map, Las Vegas is pretty much right in the middle of Flag Staff to the East and LA to the West. If Caesar doesn't stop the NCR in the Mojave, they would soon move into Arizona.

LA is like 250 miles away from Las Vegas, and the Mojave in game is rather tiny, as in the Mojave Outpost is the only part of CA in it if that.

Due to the Divide being, well the Divide, Caesar would most likely be forced to move major troop movements from what was the Mojave Outpost. In most scenarios, he would probably be fighting a losing battle.

Plus who knows how the NCR public would react to losing in the Mojave and now having an enemy on their doorstep who wants them dead.

Regardless it makes perfect sense for the Legion to be in the Mojave because the NCR is in the Mojave and it's actually a pretty ideal battlefield to fight them on given how overstretched the NCR is and how unsecured the territory they're fighting on is. The only thing the Legion does in the Mojave that is stupid is attacking the Dam directly.

The NCR is something finally large enough to challenge the Legion itself, and Caesar won't back away from the challenge. The Mojave is important to the NCR, and taking it would be an important victory. Not only that, but holding Hoover Dam (and New Vegas) is a strategic location to hold for a western conquest.

Nipton's in Cali too, and LA is only like 3 game maps away from the Mojave.

I thought for sure Goodsprings would be in California too, but it's well within the border. I was kind of surprised.