In every server there's a War Channel, usually the last channel of the server.
In war channels, opposing nations (Capella, Procyon and No Nations) names will be converted into numbers unless you have your own Chat Channel, You cannot chat or whisper with another nation in a war channel, the words would be translated into numbers and symbols. It is just like in N.Wars or Mission Wars where you kill off another player and see if you are a real master of your job.
War channels also help you prepare in your daily M.Wars. You can test your combo and damage ability, your running/escaping skills and team work against the opposing nation. Killing players and monsters in a War Channel (or War Zone) will give you Honor Points.