Although mail services have been around as long as civilizations have existed, it was not until 1840 when Britain produced the Penny Black did we see the use of pre-paid postage stamps. With these pre-paid postage's mailing items become much more efficient, and since 1840 stamps have been used for everything from propaganda to fundraisers.

• All dates are the issue date of the stamp unless otherwise noted. Some stamp series run for years!

1915, Canada, 4 Canadian Cent

• 1915, War Tax series
• In Febuary 1915 war tax stamps were issued in Canada, and were used with regular postage to pay the extra tax required to fund WW1. Many people confused war tax stamps with regular postage stamps, so in 1916 Canada just combined the war tax and regular postage stamps. So a 2 cent postage stamp may have cost 3 cent to cover the war tax.

1916, Belgium Under German Occupation, 10 Belgian Centime

• 1916, Belgium series.
• On August 4, 1914 Germany invaded the neutral Belgium after not being allowed to march its soldiers through Belgium and to France.

1922, Germany, 30 reichspfenning

• 1923, Definitive series.
• "Deutches Reich" means "German Empire", or "German Realm".

1940, Poland under Nazi Occupation, 2 Grosz

1941, Nazi Occupied Ukraine, 3 reichspfennig

• 1940, Nazi Germany occupied Poland, Overprints II series.
•  The Third Reich occupied Poland following their infamous invasion in September 1939 until 1945.

• General Edition Third Reich stamp with Ukraine overprint. 
• Nazi Germany occupied Ukraine following their surprise attack on the Soviet Union from November 1941 to fall of 1944.

1941, Central China under Japanese Occupation, 25 Sen

• Chinese Airmail stamp overprinted in Japanese currency.
• After the initial invasion of Manchuria Japan slowly gained ground in China, and in 1942 at the Imperial Japanese Army's peak Japan held more than 25% of China.

1943, Poland under Nazi Occupation, 60 Grosz

• 1943, Effigy of Hitler series
• The infamous Auschwitz murder camp was in Poland.

1948, Romania, 50 Lei.

• 1948, Economy and Transport series.
• Romania went communist in 1947, and stayed as such until 1989.

1954, Poland, 1.9 Zloty

• 1954, Protected Animals series.
• The animal on this stamp is a Chamois, which is in the same sub-family (caprinae) as sheep and goats.

1962, Ghana, 6 Ghanaian Pennies

• 1962, Accra Assembly Of Africans For a "World Without The Bomb" series.
• Accra is the capital of Ghana.
• There were numerous bombings in Ghana throughout 1962, which probably contributed to this stamp.

1968, Gibraltar, 2 Gibraltar Penny