Alliance is a bond between guilds so you could mean that I guess, but think you mean guild vs guild
Anyhow as the attacking of characters go there are several ways to go with this and even several issues that stand apart from eachother first there s the one person VS the other person, then there is the guild vs other guilds, and ofcourse roleplaying with NPCs.
I have seen planeshift and I don\'t mind that you gotta challenge someone to being able to fight someone, but seeing you don\'t gain anything from killing anyone I don\'t see what the big problem is with allowing it a little further then JUST being able to attack someone when they agree.
But how to make things so it doesn\'t turn into a newbslash game? Well first of I don\'t see it happen that often already I mean you don\'t get anything and they don\'t really die they respawn in the DeathRealm so there isn\'t that much joy to get out of that. Plus this isn\'t one of those buttonbashgames so people don\'t get much enjoyment through that way either.
Anyhow if you do implement playerfighting with more liberty to PS I think it\'s realistic to admit the game should limit it more then just the above. Perhaps there should be areas made where you can fight without having to challenge. You could make it a place where you have challenges between guilds like king of the hill or whatever tournaments you can come up with or make it so there is treasure there but it\'s not spawned that often so there are players fighting over the treasures there.
An other way might be to have people chose an alignment and have people of oposite aligments being able to fight.
You could also limit fighting to people who have about the same amount number of points trained in the fighting skillls and stats.
Plenty of ideas there I think and haven\'t even thought about how you could just make it very hard for a guildwar but not impossible without the others consent
To conclude I just want to say I don\'t want fighting on every streetcorner. I don\'t want newbs being slaughtered by the deathsquads near the spawningpoint , but I also strongly believe that having no option AT ALL to have fights without an others consent is tottally unrealistic.