Don't think of a country as an area of land. Think of a country as a club, to which a group of people belong. Nomadic tribes were not attached to any particular area of land. Settled agriculture on scarce land is a recent and contingent fact.
Clubs provide club goods to their members. Club goods are (at least partly) non-rival and (at least partly) excludable. Mutual defence is the most obvious club good that countries provide their members, but they often provide others too.
Membership of a club brings with it both rights and obligations. Membership of a club is itself a good. It's an asset that provides a future flow of benefits (and costs). Membership of a successful club, that non-members want to join, is a very valuable good. Should that very valuable good be priced at zero?