Crowfall is a MMORPG with strategy elements. You can build strongholds in the game for different purposes: you can either put strongholds into your Eternal Kingdoms or join force with other players to combine your strongholds into a single larger EK.
Strongholds are divided to various types, and estate, fort, keep, Castle have a small, medium and large version. For a given type, all three sizes will include the same amount of overall land, larger versions allow more buildings. Citadel and palace, on the other hand, do not come in multiple sizes. You can see below concept of the three sizes of fort.
While some Kickstarter backers will get their strongholds as reward, other players can purchase strongholds in the store. Besides, strongholds are transferrable to other accounts.