20th Century
| Proposed state | Components | Time period | Successful? | Notes |
|---|---|---|---|---|
| Arab Federation | Kingdom of Iraq Jordan |
1958 | Yes (14 February 1958 - 2 August 1958) |
An attempt to unify the two Hashemite kingdoms of Iraq and Jordan. While successful, the short-lived union was disestablished after a military coup deposed King Faisal II of Iraq. |
| Arab Islamic Republic | Libya Tunisia |
1974 | No | Proposed by Muammar Gaddafi. |
| Balkan Federation | Albania Bulgaria Yugoslavia |
1910 | No | |
| Federation of Arab Republics | Libya United Arab Republic Also invited: Iraq Sudan |
1972-1977 | No | An attempt to build a Pan-Arab state. |
| Franco-British Union | France United Kingdom |
1956 | No | Proposed by French Prime Minister Guy Mollet during the Suez Crisis. |
| Germany | East Germany West Germany |
1990 | Yes | German reunification |
| Greek-Serbian Federation | Greece Republic of Macedonia Federal Republic of Yugoslavia |
1992-2001 | No | A serious project proposed by Slobodan Milošević in 1992. |
| Greek-Yugoslav confederation | Strictest definition: Greece Kingdom of Yugoslavia Loosest definition also includes: Albania Bulgaria Romania |
1942-1944 | No | |
| Malaysia | Malaya Sabah Sarawak Singapore |
1963 | Yes | Singapore left the federation on 9 August 1965. |
| Międzymorze | Belarus Czechoslovakia Estonia Finland Hungary Latvia Lithuania Poland Romania Ukraine Kingdom of Yugoslavia |
November or December 1918 | No | Also called "Intermarum". Suggested shortly after World War I to combat the influences of Germany and Russia. |
| North Borneo Federation | Kingdom of Sarawak British North Borneo Protectorate of Brunei |
1956-1960 | No | |
| Polish-Czechoslovak confederation | Czechoslovakia Poland |
1939–1948 | No | A serious project proposed by Władysław Sikorski. |
| Senegambia Confederation | The Gambia Senegal |
Between 1 January 1982 and 30 September 1989 | Yes (1 January 1982 - 30 September 1989) |
Loose confederation was formed, but ended due to Gambia's lack of interest in integration. |
| Soviet Union | Byelorussian SSR Russian SFSR Transcaucasian SFSR Ukrainian SSR |
1922 | Yes (1922 - 1991) |
Treaty on the Creation of the USSR |
| Tanzania | Tanganyika Zanzibar |
1964 | Yes | |
| Ukrainian People's Republic | Ukrainian People's Republic West Ukrainian People's Republic |
1919 | Yes (1919) |
Act Zluky |
| Union of African States | Ghana Guinea Mali |
1958 | Yes (23 November 1958 - 1962) |
The Union fell apart in 1962, when Guinea started to reach out to the United States, against the Marxist leaning of the other partners, who were more oriented towards the Cold War adversary of the U.S., the Soviet Union. |
| United Arab Republic | Egypt Syria |
1958 | Yes (22 February 1958 - 28 September 1961) |
A short-lived Pan-Arab state. |
| United Arab States | United Arab Republic North Yemen |
1958 | Yes (8 March 1958 - 26 December 1961) |
Loose confederation between United Arab Republic and North Yemen. |
| Vietnam | North Vietnam South Vietnam |
1976 | Yes | |
| Yemen | North Yemen South Yemen |
1990 | Yes | |
| Kingdom of Yugoslavia | Kingdom of Montenegro Kingdom of Serbia State of Slovenes, Croats and Serbs |
1918 | Yes (1918 - 1992) |
Creation of Yugoslavia |
Read more about this topic: List Of Proposed State Mergers, Historic