In the Guild Wars tab all of the guild's members will see a list of active guild wars. Members with guild leader permissions may also create, accept or cancel/surrender wars.
To create a new war, press the Create New War button on bottom right. A new dialog will open up, where you enter the name of the opponent guild, the war duration (in days, between 1 and 30), the loss fee (between 0 and 10 million gold) and whether the war should have loyalty code enabled. Duration is the amount of days the war will last after it has been accepted, although it might end earlier if one of the guild's decide to surrender. The loss fee is paid immediately when creating a war by the war initiator, and immediately by the leader of the accepting guild when accepting the war.
A war will expire automatically if it is not accepted within 24 hours. If the war is not accepted, or results in a draw, a top position leader of the initiating guild will receive the loss fee money back in their bank balance. If a war is won, the winning guild's top leader receives the loss fee of both guilds on their bank balance. If a war has loyalty code enabled, no members may be invited or kicked from a guild after the war has been accepted. Note that players who have been invited prior to the start of the war may still join the guild. A guild may initiate at most 4 wars at a time, however, the amount of challenges received is not limited.
During an active guild war members of the opposing guild are marked with an orange skull and may be killed without counting towards your unjust kills. A war is won if either guild surrenders after a war has been accepted, or when the time limit expires and either guild has more frags than the other guild. Note that a guild war will always result in a draw if the total amount of frags is under 20 after the time limit has expired.