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The difficultity of having terriory related battle is that there will be so many darn guild in the same world, and all is instanize. Its a hard concept to sell (would be better if can have visual, verbal, body motion, and a better English teacher

Anyhow, I mad this map for better explaintion.(the map is only for tha purpose, and for simplicy, only show 2 faction) Guild, when they form, have to pick a faction (they could move between) which will also first determain where their First Guild Hall is. (they could also own the other guild hall in other place in the future, with cost, if they want). Now, they would need to declear a special Guild Territory War against another of differnt faction. Once start, guild can choose to move to differnt terriorty within movible range (one next to). They could also split the team into differnt terriotry as well. A "new" territory, one where you first came to, will be pouplar with mobs and a "goal" to conqure that territory (mostly capture some flag). Once conqure, they team could move on from it, and spawn there (as well as other advantages) So you would go and try to push on till you get to other teams guild hall. To win, conqure their guild hall. This will give your faction accumitive points in over all to determain the reward. So this type of battle is only between two Guild, and not affect by other when they are battling.
Now, so what do you do when they meet? I am not too sure if GW allow "dumping" (where dump another team into a map in the middle where other team was playing) If not, another way I could think of is this. In each battle field, there some number of "check points" to conqure. So if one team is playing, and they conqure up to check point A, and when another team enter, the map will restart, but that team can start at check point A (thus giving them some advantage) Guild team can move out of their map and to another territory to support and defend the incoming threat of another team (but will lost all their progress in that map, unless the conqure it)
About Territory and Battle Field. They are not really part of the exploration area, but special area bared for purpose of such battle. (can be overlay and exist in "another dimision" if space is problem). Thus the monster there will be kept in balance. Once a "Faction" wins a terriorty, that part of exploration area will hang its flag, as well as other possible advantage/reward/showing off. Also in next territory battle, that part will be more easily conqure and defend for the owner faction guild.
There are still many things not cover yet, like death penality, abuse, and all other stuff, but of course this is only a concept and would reqire lots rework and mod to the full game, as well as lots testing, to get it to work.