I wanna hear your opinions about how the word would be if caesars legion marched on the whole of USA,with the ncr crushed inside its boots,how life would be?

Well if it were conquered by the legion most of the population would be slaves while others would be legionary recruits

It'd be pretty much be summed up by this mod - http://www.nexusmods.com/newvegas/mods/59878/?

Pretty much as said above. They would cut a path of violence and destruction across the country. More than likely they would tackle some of the bigger factions they find along the way first. The strongest and most useful, they would make alliances with through blackmail or otherwise. The weaker groups they would enslave or kill and anyone else would be recruited to bulk up their numbers.

All in all not a happy place to live if the Legion were in charge.

As is mentioned and discussed within the game if you chase the right conversation and dialog, the Legion would most likely consume itself just like ancient Rome fell apart.

The only cohesive force behind it is Caesar's charisma and personality. With no enemies left to conquer it would turn in on itself and collapse.

Imagine, if you will, a professional sports team. They've won every single championship so often that there are no more teams to compete with. Every time they defeated a team, they took on their best players and turned the rest into cheerleaders and water boys.

Suddenly, the coach holding the team together, in a world without any competitors takes ill. Not only will there be tons of maneuvering as people try to be in position to take over when the old coach dies, the only reason to even justify the existence of a team without competition would be to somehow fabricate competition or start sacrificing some of itself as the new competition to beat.

I can argue that the Legion can be the best thing that can happen to New Vegas at the end of the questline. Mainly because having a united monolith running the political and societal sphere of the world lends itself to forces that can exist to oppose the system, especially with one that uses such brute and cruel methods as the Legion. This is possibly similar to Star Wars where the Empire gets overthrown by rebels eventually leading to something better in the long run.

On the Legion, yes they are a bunch of sick rabid pigs. But I feel as though had their quest line actually had the time to be finished, from the folks at Obsidian, we may have been able to see their full potential. Because of the game being rushed their side of the story was never fully fleshed out. Yet, out of the factions, do I believe that the Legion would have been best? Well yes and no. There of course is aspects that the Legion have that are quite a conundrum. Foremost being that they are a group of slavers, technically. Now if we were to simply go off the fact that New Vegas needs unity and a functioning system, the Legion would win. Not for the fact that the Legion uses slaves, but for the fact that they are great at unity and keeping that said unity in check. As the Roman Empire fell, so would the Legion. Out of sheer dominance, Caesar would overextend his army, and there will be someone there who takes advantage of that and finishes them off.

IIRC, one of Caesars goals was to create a "Rome" when he took New Vegas. If this happened, I believe it would alleviate some of the cultural needs of the Legion, giving them more to believe in and fight for beyond Caesar. If it works out, and Caesar has a line of succession or makes the Legion a Republic, the Legion could better rival the NCR.

If legion won and took New Vegas as his Rome, well one good thing would be crime would come to almost non existent. They don't believe in drug use so they would most certainly exterminate the Feinds. As said Legion land is some of the safest lands a courier could travel. If Legion won the battle of Hoover Dam and took Vegas then took over America. I think the death of Ceaser would not be as big a blow on Legion, and with a central Capital I think Legion could last with new leaders. I think the only reason they are doomed to fall apart is with the early demise of Ceaser and their defeat at the Hoover Dam battle.
Although I do enjoy slaughtering Legion and them being slavers is not good so destroying them is even more a plus. But Legion can tame the Wastes just is a harsher more strict way.

Oh and actually this topic makes me think of the Darkest Hour Mod Fallout Doomsday. You could play Legion and try to take over America. We could find out how that will work...

The legion would continue to expand until eventually internal trouble, combined with civilian unrest and a powerful enemy brought it to its end. Much like the actual Rome

I think that if they eventually defeated the NCR and amassed enough power to take over the U.S. they'd keep up to annex the Canada/Alaska area, and expand south.

In all honesty put it this way say they win killing all that oppose them. Lets take our courier out off the equation, cross of the NCR, Botherhood and Followers etc they win. Ok now put aside all the legions agendas, put aside Caesar's personal will. Now lets add to the point of how many will join their ranks making the legion almost a critical mass super structure. Ok so couriers gone ether way even if he/her was or wasn't there and Caesar will die due to his illness leaving the legion rule up for grabs causing the whole structure to topple. Just like Ulysses said if you don't learn from history your doomed to repeat it (Bear-Bull). That's why both are bad. But even if the legit took over during the war the legion would obtain many powerful and right to rule candidates who would rival him. Legion over

The legion is a marching force, specialized in war and destruction. As previously stated I doubt the legion would last very long if they managed to conquer the rest if the american wasteland. If they were to survive they would have to implement a different regime. The american wasteland is too big to control for the now existing legion