The Kingdom of Prussia (successor state to the Duchy of Prussia, predecessor state [ultimately] to the current Federal Republic of Germany) encompassed a whole swath of central and northern Europe for roughly half of the second millennium AD, and was a state of the German Confederation in its many iterations. The Kingdom of Prussia ceased to exist after the fall of its final king, Wilhelm II, in 1918.
Stamp details:
Stamp on left:
Issued on: October 1, 1861
From: Berlin, Kingdom of Prussia
MC #14
Stamp on right:
Issued on: July 1, 1867
From: Berlin, Kingdom of Prussia
MC #23
Recognized as sovereign states by the UN: No
Claimed by: Kingdom of Belgium; Czech Republic; Kingdom of Denmark; Federal Republic of Germany; Swiss Confederation; Republic of Lithuania; Republic of Poland; Russian Federation
Member of the Universal Postal Union: No