>When a sovereign leases territory from another sovereign, that's
>minimally, a sharing of sovereigny, or a devolution of operation of
>sovereignty to the lessee by the lessor who then
>remains only the titular sovereign.

My guess is that it very much depends on the terms of the lease. Few would
argue that the US exercises de-facto sovereignty over Guantanamo Bay,
whereas it exercises much less control over (say) Diego Garcia.

Another case is when a territory is transferred to another country, but
that country cannot subsequently transfer it to a third-party. One of the
best examples is Gibraltar which is under UK administration, but according
to the Treaty of Utrecht (1713) must be returned to Spain if relinquished.
Therefore, the UK arguably doesn't have full sovereignty.

>Was that really an international border or an administrative line.

What's the difference? I would argue that an administrative line becomes an
international border when it separates two or more entities defined by ISO
3166-1 as countries or territories.

Regards,

Kevin Meynell