Second Battle of Hoover Dam

The  is the colloquial name applied to the second offensive mounted by Caesar's Legion against New California Republic forces entrenched on Hoover Dam in 2281, as well as on the general Mojave Wasteland.

Prelude
After the First Battle of Hoover Dam, Mr. House knew that as soon as either the NCR or the Legion became victorious at the Dam, they would turn their attention to New Vegas. In an attempt to stop this and allow the city remain under his control, he had Victor hire a courier to retrieve his Platinum Chip, a data storage device capable of upgrading the city's defense systems and activating a massive army of PDQ-88b securitrons, which would give House the ability to single-handedly crush the Legion and intimidate the NCR into a retreat. However, the leader of the Chairmen, Benny, learned of this plan and ambushed House's Courier outside of Goodsprings, shooting him in the head and leaving him for dead in a shallow grave and taking the Platinum Chip, throwing House's plans into disarray.

The Courier survived, however, and began a journey to the New Vegas Strip to find Benny and get revenge, in the process learning the true purpose of the Platinum Chip and its power. The Courier was faced with the choice of either giving the Chip to House or destroying the securitron army, or even using it to create an army of their own. The Courier's journey attracted the attention of the NCR and the Legion, both wanting such an influential individual on their side, although which side (if either) the Courier chose remains lost to history. In preparation, the Courier traveled the land looking for tribes to ally with, but again, which allied with the Courier, which did not, and which were even outright destroyed is unknown.

Hoover Dam
The player's role in the battle depends greatly on which faction they have sided with. Mr. House's and Yes Man's quests are very similar, both involve activating the Securitron army. From there, you will have to fight across the dam to the Legion camp on the other side of the dam. The NCR quest will have you do the same basic thing; fight through enemy forces to get to the other side of the dam. While traversing the dam, you will notice the aid promised by any factions you gathered support from. Once you get across the dam, you will get to Legate's Camp, having to face off with Legate Lanius. You can fight, or pass a series of difficult skill checks and avoid combat. From there, you return to the main gate, where it will be blown down by General Lee Oliver and his men. If fighting for the NCR, he will congratulate you. If fighting for Yes Man/Mr. House, you will have the choice of talking him out of a final confrontation, or proceeding with attacking him - with the help of your new shiny Securitron army. Either way, the game ends there.

If fighting for the Legion, the battle is similar to the NCR's quest, only in reverse. You start in Legate's camp and fight across the dam to the NCR side. The final confrontation is still with General Lee Oliver. If you can pass a high skill check, you can talk him out of fighting, but otherwise you will have to kill him.

Elsewhere
The details of the battle at Hoover Dam are unclear, however the fighting was not just limited to that relatively small location; violence engulfed the entire Mojave Wasteland as Legion forces and its allies attacked NCR targets and locations across the region, with varying levels of success:
 * The NCR Embassy on the New Vegas Strip was bombed, and if they had not been stopped by the Courier already, the Omertas attempted a coup but were stopped by the Chairmen and the White Glove Society, as well as the securitrons.
 * Rioting broke out in Freeside (although its severity is unclear; if the Courier forged an alliance between the Kings and the NCR, the riots were much more tame).
 * The Fiends attacked Camp McCarran, but if the Courier killed their leaders beforehand, they are easily defeated.
 * Camp Forlorn Hope was attacked by the Legion, but if 1st Recon were present and the Courier managed to solve the camp's many problems, the NCR soldiers were able to fend off the attack.
 * The Frumentarii made an attempt to bomb the monorail outside McCarran, whether it was successful or not depends on whether the Courier uncovered their plot or not.
 * Camp Golf was attacked, but the Legion were easily defeated by the Misfits (if they were trained by the Courier, otherwise Chief Hanlon and the other rangers stationed there were crucified).
 * Novac was attacked by the Legion and many of its citizens were said to have died in its defense, but if the Bright Brotherhood was aided in starting on their pilgrimage, they returned in time to help rebuild.


 * At a location known as "Bravo Bravo Charlie", a doctor arrived.
 * They're coming out of the walls man! They're coming out of the damn walls!

Appearances
The is the finale of Fallout: New Vegas.