1) A war isnt actually declared. One guild is challenged by another and the guild leader will either accept the challenge or not. Quite often this decision is made soley on how many guild members are currently online.
2) Yes you lose xp if you die in a war. So take suitable precautions so as not to die. (use auto-potion, use the right potions, use scrolls, etc)
2a) I'd have to assume you lose SP too, but I was so annoyed at being dead I didnt pause to check that.
3) No you dont get murderer status if you kill someone after the war officially starts. A war lasts for one hour. Although a guild leader can end the war early by forfieting. (the other guild would then be declared the winner of course)
What you do get is "contribution points" when u press u, one of the tabs will show you how many contribution points other guild members have. The ones that have more are usually the ones who are more dangerous.
4) The point is usually to settle a score, or simply to prove that your guild can beat the other.
5) Yes you can get $$ for winning a war. Before the war begins, there is an option for "compensation" that can be selected. Both guilds must agree to the terms before the war begins. Then the loser must pay the compensation to the winner after the war has finished.
Having said all that, understand this.
There are no rules!! Expect to be attacked by multiple opponents, expect to be attacked by someone 20 lvl's higher than you, expect that they will not wait until you have "powered up" and are "ready now".
If you see someone from the opposing guild, target them whilst they are still in the "safe zone", and if so much as their big toe steps across the line, unleash blind fury.
Thats the only rules you need concern yourself with, the guild master will handle the rest.
