Recently, Black Desert unveiled a new gameplay video showcasing various combat and battlefield scenes in siege war.
There are two kinds of siege which are castle siege and citadel siege. Citadel siege is acctually territory warfare.
Guilds should build up their symbols which are something like command centers or fortresses before the siege begins at a specified time. Some NPCs can be employed to build a symbol with woods, stones etc. and it usually takes 1-2 days to complete the symbol. When the symbols are completed, they can join in the siege. When the symbols are destroyed during the siege, the siege ends.