Is siege combat only available in the Border Kingdoms?
No, siege combat actually comes in three variations. One for the Border Kingdom where guilds will use catapults, trebuchets and other siege engines to fight over a battlekeep, and two for the player city areas where the player city can defend their own city with siege engines as well as attack the neighboring computer-controlled city that will build up next to it. So you will basically find siege combat in the Border Kingdom as well as in the player city areas, but only the former include PvP siege combat where players dish out against each other over ownership of the battlekeeps.
