The Guild Domain is a new mechanic introducted in the War Under Shattered Skies update (2.6.002) that focuses on decorating your domain with decors (In the same fashion as decorating and expanding your Kingdom.) The Domain begins with a few spaces, but can be expanded similarly to the Kingdom.
Decors can be purchased at the Guild Shop, much like the Decor Shop, but with a difference. Rather than placing the decor for yourself, only guild members that are Decorators can place the decors only in the Guild Domain.
The Guild Domain is separated into three modes: the Guild Hall, the Guild Museum, and the Cookie Alliance mode.