A buffer state is a country lying between two rival or potentially hostile great powers. Its existence can sometimes be thought to prevent conflict between them. A buffer state is sometimes a mutually agreed upon area lying between two greater powers, which is demilitarized in the sense of not hosting the military of either power (though it will usually have its own military forces). The invasion of a buffer state by one of the powers surrounding it will often result in war between the powers.
Research shows that buffer states are significantly more likely to be conquered and occupied than are nonbuffer states. This is because "states that great powers have an interest in preserving—buffer states—are in fact in a high-risk group for death. Regional or great powers surrounding buffer states face a strategic imperative to take over buffer states: if these powers fail to act against the buffer, they fear that their opponent will take it over in their stead. By contrast, these concerns do not apply to nonbuffer states, where powers face no competition for influence or control."
Buffer states, when authentically independent, typically pursue a neutralist foreign policy, which distinguishes them from satellite states. The concept of buffer states is part of a theory of the balance of power that entered European strategic and diplomatic thinking in the 18th century.
- Bolivia, created by Gran Colombia as a buffer between Peru and Argentina during the Upper Peru question.
- Uruguay, served as a demilitarized buffer between Argentina and the Empire of Brazil during the early independence period in South America.
- Paraguay, maintained after the end of the Paraguayan War in 1870, as a buffer separating Argentina and Brazil.
- Georgia, a colony established by Great Britain in 1732 as a buffer between its other colonies along the Atlantic coast of North America and Spanish Florida.
- Ecuador, served as a "cushion state" between Colombia and Peru, which had a bigger extension and military force and fought a war in the 1820s in what is now Ecuador.
- Multiple buffer states played major roles during Roman–Persian Wars (66 BC – 628 AD).
- North Korea during and after the Cold War, seen by some analysts as a buffer state between the military forces of China and U.S. forces in South Korea, Japan and U.S. fleet in Taiwan.
- Manchuria was a pro-Japanese buffer state between the Empire of Japan, the Soviet Union, and Republic of China during World War II.
- Siam, whose king had to surrender his country's hegemony over Laos and Cambodia and to grant commercial concessions to France but managed to retain independence as a buffer state between British Raj, British Malaya, and the French Indochina.
- Korea was acting a buffer zone between the growing superpower, Empire of Japan and the northern mainland neighbor, Russian Empire.
- The Far Eastern Republic was a formally independent state created to act as a buffer between Bolshevik Russia and the Empire of Japan.
- Afghanistan was a buffer state between the British Empire (which ruled much of South Asia) and the Russian Empire (which ruled much of Central Asia) during the Anglo–Russian conflicts in Asia during the 19th century, with the Wakhan Corridor later extending the buffer eastwards to the Chinese border.
- The Himalayan nations of Nepal, Bhutan, and Sikkim were buffer-states between the British Empire and China, later between China and India, which in 1962 fought the Sino-Indian War in places where the two regional powers bordered each other.
- Mongolia, acted as a buffer between the Soviet Union and China until 1991 and currently serves as a buffer between Russia and China.
- Lebanon is a buffer state between Israel and Syria.
- Morocco served as a buffer state between the Ottoman Empire, Spain, and Portugal in the 16th century.
- The United Kingdom of the Netherlands, composed of today's Belgium and Netherlands and created by the Congress of Vienna in 1815 in order to maintain peace between France, Prussia and the United Kingdom. This state existed for 15 years until the Belgian revolution.
- The Rhineland served as a demilitarized buffer-zone between France and Germany during the inter-war years of the 1920s and early 1930s. There were early French attempts at creating the Rhineland Republic.
- The Socialist Soviet Republic of Byelorussia was founded as a buffer state between Soviet Russia and European powers.
- Qasim Khanate, between Muscovy and Kazan Khanate.
- Austria acted as a buffer state between Germany and Italy after World War I until 1938.
- Poland and other states between Germany and the Soviet Union have sometimes been described as buffer states, with reference both to when they were non-communist states before World War II, and to when they were communist states after World War II.
- Yugoslavia acted as a buffer state between NATO and the Warsaw Pact blocs after the 1948 Tito-Stalin split during the Cold War.
- Ukraine has been described by experts such as John Mearsheimer and Stephen Walt as a buffer state between Russia and the NATO bloc, at least up to the ousting of former President Viktor Yanukovych in February 2014.
- Switzerland was made as a buffer state between Italy, Austria, France and the German states.
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Chapter 25: Destruction of the Buffer States between Germany and the Soviet Union.
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Moscow's German Problem before Detente - The Federal Republic - In 1945, the major Soviet preoccupation was to prevent any future German attack; hence the imposition of Soviet-controlled governments in a ring of buffer states between Germany and the USSR.
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Washington has a deep-seated interest in ending this conflict and maintaining Ukraine as a sovereign buffer state between Russia and NATO.
- Walt, Stephen M. (2 September 2014). "History Shows Caution Is the Best Approach for Foreign Action". The New York Times. Retrieved 1 January 2015.
Instead of rushing to back the demonstrators who ousted the former president, Viktor Yanukovych, the United States and its European allies should have worked cooperatively with Moscow to craft a deal that would have preserved Ukraine’s status as an independent but neutral buffer state.