Sphere of influence
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In the field of international relations, a sphere of influence (SOI) is a spatial region or concept division over which a state or organization has significant cultural, economic, military, or political influence.
While there may be a formal alliance or other treaty obligations between the influence and influencer, such formal arrangements are not necessary and the influence can often be more of an example of soft power. Similarly, a formal alliance does not necessarily mean that one country lies within another's sphere of influence.
In more extreme cases, a country within the "sphere of influence" of another may become a subsidiary of that state and serve in effect as a "satellite state" or "de facto" colony. The system of spheres of influence by which powerful nations intervene in the affairs of others continues to the present day. It is often analyzed in terms of superpowers, great powers, and/or middle powers.
For example, during the height of its existence in World War II, the Japanese Empire had quite a large sphere of influence. The Japanese government directly governed events in Korea, Vietnam, Taiwan, and parts of China. The "Greater East Asia Co-Prosperity Sphere" could thus be quite easily drawn on a map of the Pacific Ocean as a large "bubble" surrounding the islands of Japan and the Asian and Pacific nations it controlled.
Sometimes portions of a single country can fall into two distinct spheres of influence. In the colonial era the buffer states of Iran and Thailand, lying between the empires of Britain/Russia and Britain/France respectively, were divided between the spheres of influence of the imperial powers. Likewise, after World War II, Germany was divided into four occupation zones, which later consolidated into West Germany and East Germany, the former a member of NATO and the latter a member of the Warsaw Pact.
Historical remnants 
Many areas of the world are considered to have inherited culture from a previous sphere of influence, that while perhaps today halted, continues to fool people into using this as a primary source of information. Examples include the Anglosphere, Arab World, Eurosphere, Francophonie, Françafrique, Germanosphere, Indosphere, Latin Europe/Latin America, Chinese cultural sphere, Slavisphere, as well as many others.
Molotov-Ribbentrop Pact 
According to a secret protocol attached to the Molotov-Ribbentrop pact of 1939 (revealed only after Germany's defeat in 1945), Northern and Eastern Europe were divided into Nazi and Soviet "spheres of influence". In the North, Finland, Estonia and Latvia were assigned to the Soviet sphere. Poland was to be partitioned in the event of its "political rearrangement"—the areas east of the Narev, Vistula and San Rivers going to the Soviet Union while Germany would occupy the west. Lithuania, adjacent to East Prussia, would be in the German sphere of influence, although a second secret protocol agreed in September 1939 assigned Lithuania to the USSR. Another clause of the treaty was that Bessarabia, then part of Romania, was to be joined to the Moldovan ASSR, and become the Moldovan SSR under control of Moscow. This division into spheres of influence lasted less than two years, and ended when Germany invaded the Soviet Union in 1941, in violation of the non-aggression pact.
Cold War 
During the Cold War the Baltic states, Central Europe, some countries in Eastern Europe, Cuba, Laos, Vietnam, North Korea, and, until the Sino-Soviet split, the People's Republic of China, among other countries at various times, were said to lie under the Soviet sphere of influence. Western Europe, Oceania, Japan, and South Korea, among other countries, were often said to lie under the sphere of influence of the United States. However, the level of control exerted in these spheres varied and was not absolute. For instance, France and Great Britain were able to act independently to invade (with Israel) the Suez Canal (they were later forced to withdraw by joint US and Soviet pressure). Later, France was also able to withdraw from the military arm of the North Atlantic Treaty Organisation (NATO). Cuba often took positions that put it at odds with its Soviet ally, including momentary alliances with the People's Republic of China, economic reorganizations, and providing support for insurgencies in Africa and the Americas without prior approval from the Soviet Union.
With the end of the Cold War, the Eastern Bloc fell apart, effectively ending the Soviet sphere of influence. Then in 1991, the Soviet Union collapsed, replaced by the Russian Federation and several ex-Soviet Republics became independent states. Much of the diplomacy since in eastern Europe, the Caucasus and Central Asia has revolved around which countries are in whose sphere of influence.
United States 
Russian Federation 
Other examples 
For historical and current examples of significant battles over spheres of influence see:
When talking in corporate terms, the sphere of influence of a business, organization or group can show its power and influence in the decisions of other business/organization/groups. It can be found using many factors, such as the size, the frequency of visits, etc. In most cases, a company described as bigger has a larger sphere of influence.
For example, the software company Microsoft has a large sphere of influence in the market of operating systems; any entity wishing for its software product must ensure that it is compatible with Microsoft's products to be successful.
For another example, for companies wishing to make the most profits, they must ensure they open their stores in the correct location. This is also true for shopping centers that, to reap the most profits, must be able to attract customers to its vicinity.
There is no defined scale on how to measure the sphere of influence. However, the spheres of influence of two shopping centers, two business canmeasured by seeing how far people are prepared to travel to the shopping center, how much time they spend in its vicinity, how often they visit, the order of goods available, etc.
In a geographical meaning, a sphere of influence is the average distance people are willing to travel to get to a particular service, shop, or place. It can be displayed as a diagram of a circle centered around the service, with the radius being the average distance people would travel to get to that service. The distances travelled are often found out by the use of a survey. This is also related to Cristaller's Central Place Theory
See also 
- National interest
- Balance of power in international relations
- Lateral Pressure Theory
- The CommonCensus Map Project – Calculates the spheres of influence for American cities based on voting
- Russia - a counterbalancing agent to the Asia.