This is where the guide about Blue war will appear.

What is Blue War?You are called upon to defend your village or city from being conquered by the evil forces!
When can I start Blue War?Blue War takes place every full hour. (12:00 GMT, 13:00 GMT, etc)

Blue War alternate between Lower (lvl 11-15, 16-20, 21-25, 26-30, 31-35 and 36-40) and Higher (Lvl 41-50, 51-60, 61-70, 71-80, 81-90 and 91 and up)
Each one of these occurs approximately every 12 hour sequence.
After keeping records of 2 days of Blue War data, it's clear that the pattern is not totally random, but it is not predictable either. As I mentioned above, it seems that most of them occur twice a day. Theory is: same wars occur 8, 10 or 12 hours after the same previous one.
Lower Blue Wars originate from the villages, while higer Blue Wars originate from the cities.

How do I win?Kill all the demons within 55 minutes time. If all players are killed, or demons are still alive after 55 minutes, the war is lost. You get some fame and keep any items you got during fighting though
Is there a difference in Demon types between cities and between villages?Supposedly yes, but more information is needed.
What can I expect to fight in villages?Dark Captains, each with a different sized army
What can I expect to fight in cities?Dark Captains and Dark Commanders (much harder to kill, have a lot of dex too)
What can I get from Blue War?Mystery Boxes, Another Kind of Boxes and Magical Boxes which can be opened in Ilium at the jeweler, inside can be the most common things like chicken, or nice things like potions, or ores, or a dance-scroll, fighting doll, durable exp doll, advanced fighting doll, pet dolls,

Bluebird war is the Rosen lake map
bwar
Red dots are Demon spawn points

Rainbow City war is the Western Grasslands map
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Red dots are Demon spawn points

Goldburg war is the Genie Desert map
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Red dots are Demon spawn points

Gion
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Red dots are Demon spawn points

Greenville
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Red dots are Demon spawn points

Ilium
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Red dots are Demon spawn points

Thanks to Laun, Moiraine, Nishihara & Endril