Ive been looking at the videos of the three factions and the way it seems is

Mr. House - hates NCR

NCR - hates Casear's Legion

Casear's Legion - hates House

so if this is true it'd mean

Side with House and at the end of the storyline - you kill Dennis Crocker = leaving NCR with no leader, and demoralized.

Side with NCR and at the end of the storyline - you kill Casear = Stopping Casear's conquering of the mojave wasteland.

Side with Casear's Legion and at the end of the storyline - you kill Mr. House = Causing the families to vie for control of the strip.

This could be the reason why you cant continue after you beat the story, because there'd be no more war and everything would almost go back to normal(boring).

I'm hoping it's slightly more complex than "kill their leader" and more like "destroy what their leader cares about." Nuke this place, destroy this other place, etc. Like, you could take out the Hoover Dam for one faction to deny another their electricity or something. Which is a pretty big blow and drastic change. This would be a reason to not continue, as they've stated that their ending(s) would require extensive new content. If you took out one group's power, then you'd not only have to change all their light maps, but you'd have to change all their voice over dialogue to them complaining about how they have no lights and maybe explain why they're sitting in pitch black rooms instead of setting up new operations.

i guess we'll never know...

oh wait... we will. my bad.

I don't think it's that simple- house doesn't hate NCR or he wouldn't let them wander drunkenly around his city.
It's more that he doesn't trust NCR fully. It could go both ways.

What I want to do, is to take that seed of distrust, and let it bloom into a tree of hate against NCR. Just for [censored] and giggles

kill mr house side with yes man and side with ncr that how i think im going to do it

Im a Man of Two War's
i Want To Join Ceaser's Legion but at the Same time Join Mr.House

Ill Go with Mr.House for His Penthouse And Snowglobe Prices

And The Legion For all My Evil needs >.>
<.<

All with fall under the might of the courier.