pre game alliances...

[Legendary League]

How does one create an alliance before the game, when starts are random?

As for in-game alliances and coalitions, they form naturally, and are common pretty much everywhere as a natural extension of power politics (only difference is that these alliances will almost never last till the end of the game).

In the same game you've talked about, BSoD, I started out trying to organize a coalition against Bogarus, before having the same treatment served back to me as Pangaea and Bogarus tag-teamed me as an extension of their own geographic location and strategic interests (for Pangaea, he could either go for me or Midgard, and I offer no strategic overstretch [plus Marignon is a bummer for Pangaea later on anyways[, while Bogarus caught wind of my attempts at preemptively halting his insane gold/research curve from curving, and so was able to organize his own alliance against me (whilst his neighbors were busy with you to the south). Meanwhile I convinced Midgard that a Pangaea who took all of my lands would have only one other target to go after, and thus formed a pseudo-alliance with hi, (it was never formalized or vocalized, but we maintained our NAP and both fought Pangaea).

Fighting multiple nations at once will happen, and I will say without a doubt that none of them are ever formed before the game starts, since no one knows where everyone will start to begin with, and who they're facing. You can't forge an alliance between Vanheim and Helheim against Niefelheim pre-game, say, because chances may be that all three nations start at opposite corners of the map (or, say Vanheim would benefit greatly from attacking Helheim if they were neighbors).

This is coming from an International Relations major, and someone who's played thus far some MP games.