The domain of King’s Landing operates differently than other domains. First, you must control at least 3 Castles to either march or sail into it, and you may not retreat into it if it is unoccupied.
When you meet the 3 Castle requirement, only then can you move into King’s Landing and gain the Iron Throne, adding it to your Ally Pool. Having it offers these benefits:
• The Iron Throne is a “wild” Power Token in your Ally Pool, meaning sitting on it counts as 1 Power Token for every non-player house.
• When King’s Landing is attacked, it offers 2 () in defense.
• You gain during a scoring round if you have enough units recruited (see Scoring Phase).
• Ally Power Tokens may occupy King’s Landing with you, but be careful—losing that alliance means that you must retreat.
If you no longer control 3 Castles then you must immediately retreat from King's Landing (see Retreating). Then return the Iron Throne to its spot on King’s Landing.