Northfort is a city of ice where live the Barbarian Army. You can conquer this town for you, and to become leader of the Barbarian Army, so you can invite your friends or kick old members. But for this you must do a mission, you have to prove that be able to join the barbarians, killing his guardian. It is of utmost importance to emphasize that this mission can only be done once a day and guild leader must be online.
Conquering the castle: First go to the island of teleports, south of the island you will find the room of the conquests. Note that to conquer Northfort have requirement of level 150. Move the switch, then you summon the guardian Barbarian_Leader, now go to Northfort (north of the city, climb the stairs toward the castle, the left where are the guardian) and kill him, when you kill the guardian appear a focus crystal, get it and enter the castle, and enter the throne room. Once you're there, put the crystal on the pedestal (marked in the image in pink) and pull the switch. The guild should be yours.
Inviting players: In the throne room inside the castle, the player must step on the stone tile marked in the image in yellow and the leader moves the switch.
Kicking old members: Talk to your henchman, if you need to "Prison" old guild leader and his followers.
Leaving guild: Only move the switch marked in green in the image.