Eminent domain comes from English common law. The crown ultimately owns everything (i.e. holds eminent domain). Your "fee simple" property allows you to hold ri

Eminent domain comes from English common law. The crown ultimately owns everything (i.e. holds eminent domain). Your "fee simple" property allows you to hold rights in the property in perpetuity in exchange for a simple fee (as opposed to a lease). The crown still holds eminent domain, however, and can take it away. The "constitutional" part of "constitutional monarchy" does create a process and establish compensation and such so that your rights can't be taken away arbitrarily.