Political maps change, and flags disappear when countries are dissolved, united, occupied or replaced by new states.
The Soviet Union
The red flag with the hammer, sickle and star became one of the most recognisable symbols of the twentieth century. It ceased to be the flag of a country when the Soviet Union dissolved in 1991.
Yugoslavia
Yugoslavia used several versions of a blue, white and red tricolour, including designs featuring the communist red star. The state eventually broke apart into several independent countries.
Czechoslovakia
Czechoslovakia used a white-and-red design with a blue triangle at the hoist. The country peacefully split into the Czech Republic and Slovakia in 1993.
East Germany
The German Democratic Republic used the black-red-gold German colours with a state emblem. After German reunification in 1990, the East German flag ceased to be a national flag.
Why old flags still matter
Historical flags remain important because they help explain the political history of places that no longer exist as independent states.