There's a lot to this story, but some of it is being left out.
1. Nova dominated the server, had the biggest zerg.
2. MS did indeed yes have two parties, what they aren't openly telling people is this. They sieged, yes. They dropped all wars and stopped attempting to even xp, they fished to 105. This made MANY of the top nova players quit.
3. MS was so desperate to topple NOVA, which they did partially because of truffle one shotting everyone, every time, and partially due to people getting bored and quitting that they mass recruited anyone, from both servers.
4. Most of the people in MS now weren't even around for this, so they have no idea, they jumped ship joined the top dog and want pvp.
5. MS is getting frustrated due to lack of pvp, boring sieges. Guess what else isn't fun? Having two decent parties, and fighting 5, then having another 5 port in on top of you. Why waste my time? You guys say you want pvp, say you want sieges. Every, single, time i have ever fought ms this is what happens. We win, you rebuild, log all your top players trade gear for half an hour then say lets go again. You only fight when the advantage is in your court, even in sieges, one party is fighting one of ours and you don't let the fight happen. You port three additional parties.
The only way to get rid of the ms zerg? Simple. Stop engaging them, stop pvping them, stop sieging, ignore them. They will get bored of having all this gear and nothing to do and will try to form up another side, or simply will quit. It is already happening, if you guys could see the PMS from MS members you'd laugh (No I don't share PMS because I am not a 13 year old girl like choco).
P.S I am a horrible L2 player and bad at every aspect of this game, and I am a nobody. <Just to get the next 13 MS replies out of the way>