The Ross Dependency (named for British explorer Sir James Clark Ross) was originally a British claim

TheRoss Dependency (named for British explorer Sir James Clark Ross) was originally a British claim in Antarctica (from 1841), before being passed to New Zealand control in the 1920s.  Since the enactment of the Antarctic Treaty in 1961, most of the world no longer recognizes Antarctic claims, though that hardly stops anyone from claiming them anyway…

Stamp details:
Stamp on top:
Issued on: January 11, 1957
From: Scott Base, Ross Dependency
MC #1

Stamps on bottom:
Issued on: November 25, 2009
From: Scott Base, Ross Dependency
MC #114-118

Recognized as a sovereign state by the UN: No
Claimed by: New Zealand
Member of the Universal Postal Union: Yes (as a territory New Zealand)