Could Caesar have potentially made an alliance with the brotherhood? At first glance, both have egos that would want to be in charge. But Caesar betrays his alliances, so he could probably briefly play along. Both are less than friendly to really advanced technology, and both find a common and very direct and dangerous enemy in the NCR, and the brotherhood is more than capable of sporting a few dark-sides of their own. I seem to recall them using explosive collars to force assassinations some scenarios.

If there's a BOS-Caesar alliance in the game, I never saw it.

Could Caesar have done more to cut a deal with the gun runners? I'm not sure what he could have offered, but he could always have betrayed them later, so it really wouldn't matter as long as he got some kind of temporary benefit. Expecting to fight with swords against guns is just not sensible even with numbers, the cost to the legion would be unnecessarily high -- Lanius was capable of understanding that. A deal with the gun runners, if that was possible, could have changed it all.

I think Lanius saw something that Caesar did not; that the Legion was not quite ready to take on the NCR without tremendous losses -- the legion had burned down all the potential supply lines in Nipton, Nelson, and Searchlight; an incredibly foolish move, which Lanius saw and Caesar did not.

I believe there was cut content that allowed a temporary alliance with the Brotherhood. Imo it wouldn't make sense for the brotherhood, despite their status and rivalry towards the NCR, to ally with what they view as savages, much less slavers who treat women as second class. The Brotherhood are smart enough to not trust the legion, and given their reclusive and distrusting nature, they wouldn't have agreed to an alliance given the lore, which is probably why they cut it out. As for the Gun Runners, they're an NCR based trade organization that thrives in their economy. There's absolutely no reason for them to ally with the legion, as they're not an actual faction, but a group of traders that are the main source of the NCR's post-war weapons. Caesar's alliances in game were the only ones that made sense, and even then he was plotting to betray and absorb them into the Legion.

Caesar could have made more alliances, of course we all the know our beloved BoS is not one of these so called "Alliances". But Edward could of made a alliance with the Omertas. Why? the Legion could sell those female slaves to them and the customers at the Omertas' Casino could have "Sex" over there. But I also think Caesar would not like his Slaves to be treated like this, they deserve pain and suffering not relaxing and enjoyment. But I also think Caesar would make alliances with smaller groups, more like bandit and criminal typeish.

Not sure about an alliance but maybe a temporary agreement to not be hostile towards each other until they push the NCR out of the Mojave.

It is possible that the Mojave Chapter of the Brotherhood of Steel could agree to this out of arrogance(if led by Hardin) since they view the Legion as nothing more than a bunch of savages.

I do not really see them working with each other since both have conflicting agendas(one with an aversion towards technology and one who embraces it).

Any brotherhood-Caesar alliance would have to be something that would allow the brotherhood to, well, have a reason to make that alliance. It' would probably have to be a particularly creative offer, since the Brotherhood can be stubborn and thick-headed even in the face of their destruction, and probably wouldn't fall for a trick/false alliance like several other factions could.

Hell yeah he could've, if he wasn't so averse to technology, he could convince the Brotherhood of Steel for isolation and promising them the ability to scavenge pre-war ruins, too good to sound true to any practical person but for a beaten and defeated group of people, they'd take it. Caesar however would backstab them in the end almost certainly, a group with so much technological power is a threat to the Legion's power choke hold on the region, and not to mention Caesar hates technology. He could make an alliance with the Vipers and that other gang's name (Forgot it) but I think they would be so fucked up on drugs and so uncivilized, they'd kill any Legion negotiator. The final alliance I think they can make is with the cannibals in the Deluxe Casino, they were JUST squabbling tribal members merely less than a decade ago, they can become that once again. Plus, he could use their sick cannibalism against the bulwark of NCR by snatching VIPs and other things of interest under House/NCR control but since Caesar already promised the Omertas the strip, there would inevitably be a power struggle soon to come after the conquest of New Vegas (If the fuckers pulled it off, and it wouldn't happen on my watch.).