[Legendary League]

In general, there is no way to avoid fighting multiple nations at once besides shrewd diplomacy and good risk management. That is, don't get into a war if you don't think you can win (and win fast, with the least amount of casualties possible]). In the BSoD game, I believe you were willing to spark a war with Abysia over a common indy-battle over a province, without securing your flanks, which lead to Ulm falling on you some turns after. You did miscalculate with your pretender, as Cradle as a map is very much slanted towards defensive play (with the mass chokepoints and difficult terrain), but others capitalized on your weakness.

I'll use my PowerBeyondComprehension game as an example of what I mean by risk management. As Helheim, I located C'tis on an isolated peninsula as a start location with myself as the only land connection. I examined the matchup to determine that I would win handily before he hit major battle magicks, so I intensified my efforts to secure my other borders and neighbors with NAPs, while lulling C'tis into a slightly more relaxed position with an NAP-1 (i.e. warning the turn before troops march to occupy), and baited out information like research goals from PM conversations, in addition to drawing his army into disadvantageous positions and losses with unfavorable (for me) border delineations, which all added up to me being able to cripple C'tis in such a fashion that he couldn't contest my thugs and eventual army. That and (publically) whoring my svalts off for several turns forging items to fund the whole venture.