Server vs Server War occurs every two weeks (from when the previous war ends) in the servers that have qualified for it. Your opponent will be announced 72 hours before the beginning of the war and an additional server vs server chat opens up. The war will last 48 hours. You will receive 4 server teleports at the start of the war. To qualify, you must have a King claim the throne within the first 90 days of server opening. Once you have done this, you will get matched up by ranking with another server to participate in a 48 hour war event. During this time, each server gets points for a variety of different tasks.
If you kill players of the opposing server, you claim points based on the number of troops and the tier of troops that have been wounded or killed. The wounded troops go into their hospital and the dead troops are available for revival from the hospital as well. These will cost source of life tokens.
In addition to killing enemies, you can earn points by killing bosses and monsters in the enemy server, as well as hitting fairies and Ares Towers.
For many, this event is what you build for. Many servers will try to setup the timing of their throne war to ensure it does not occur during this bi-weekly event.