A civil war is a war in which parties within the same culture, society or nationality fight against each other for the control of political power.
Some civil wars are categorized as revolutions when major societal restructuring is a possible outcome of the conflict. An insurgency, whether successful or not, is likely to be classified as a civil war by some historians if, and only if, organized armies fight conventional battles. Other historians state the criterion for a civil war is that there must be prolonged violence between organized factions or defined regions of a country (conventionally fought or not).
Ultimately the distinction between a "civil war" and a "revolution" or any other name may be arbitrary, and is determined by usage. However the distinction between a "civil war" and "revolution" can be recognizable. The successful civil war of the 1640s in England which led to the (temporary) overthrow of the monarchy represented by Charles I became known as the English Civil War, which can be described, by Marxists and some historians, as the English Revolution. The successful insurgency of the 1770s in British colonies in America, with organized armies fighting battles, came to be known as the American Revolution. In the United States, and in American-dominated sources, the term 'the civil war' usually means the American Civil War, with other civil wars noted or inferred from context.
Factors such as nationalism, religion, and ideology played little role in pre-modern civil wars. Modern nationalists have commonly read past revolts (such as Scotland against England or Catalonia against Spain) as early stirrings of nationalism, the truth is that these conflicts were in fact feudal or dynastic rather than national. There are some pre-modern civil wars that can be seen as fueled by religion (the Jewish Revolts against Rome), but these can also be seen as revolts by a servile people against their oppressors or uprisings by local notables in an attempt to gain independence.
1.1 International Definition
1.2 U.S. Military Definition
1.3 NATO Definition
2 Premodern Civil Wars
2.1 Religious conflicts
2.3 Separatist revolts
3 Reasons for war
4 See also
7 External links
A civil war is "a violent conflict within a country fought by organized groups that aim to take power at the center or in a region, or to change government policies". Everyday usage of the term does not entail a clear threshold for how much violence is necessary to qualify a conflict as a civil war, as opposed to terrorism or low-level political strife. Scholars use two criteria: the warring groups must be from the same country and fighting for control of the political center, control over a separatist state or to force a major change in policy. Their second criterion is that at least 1,000 people must have been killed in total, with at least 100 from each side. Note however that other social scientists consider this casualty number rather low and prefer for instance a definition of an average of 1,000 people killed per year.
The Final Record of the Diplomatic Conference of Geneva of 1949, (Volume II-B, p. 121) does not specifically define the term ‘civil war’. It did, however, describe the criteria that separate any act committed by force of arms (anarchy, terrorism, or plain banditry) from those qualifying as ‘armed conflict not of an international character’ which includes civil wars. Among those conditions listed are these four basic requirements.
• The party in revolt must be in possession of a part of the national territory. This was most surprising.
• The insurgent civil authority must exercise de facto authority over the population within the determinate portion of the national territory.
• The insurgents must have some amount of recognition as a belligerent.
• The legal Government is “obliged to have recourse to the regular military forces against insurgents organized as military.”
The International Committee of the Red Cross (ICRC) further clarified Article 3 of the Geneva Convention. They stated that the nature of these armed conflicts, not of an international character “generally refer to conflicts with armed forces on either side which are in many respects similar to an international war, but take place within the confines of a single country.” 
U.S. Military Definition
The U.S. military has adopted the principles set by the Diplomatic Conference of Geneva for their definition of civil war. However, it does include an additional requirement for identifiable armed forces. The December 1990 version of FM 100-20 (Military Operations in Low Intensity Conflict) defines a civil war as:
“A war between factions of the same country; there are five criteria for international recognition of this status: the contestants must control territory, have a functioning government, enjoy some foreign recognition, have identifiable regular armed forces, and engage in major military operations.”
NATO does not directly define civil war. However, in the North Atlantic Treaty Organization Glossary of Terms and Definitions (Organisation Du Traite De L'Atlantique Nord Glossaire De Terms Et Definitions) NATO does provide a reference for what is not classified as a civil war. The manual states that 'civil disturbance' is defined as "group acts of violence and disorder prejudicial to public law and order". 
This definition supports the premise shared by the Geneva Convention, ICRC, and the U.S. Military that a civil is a higher level of violence commensurate with that of a conventional war of movement.
Premodern Civil Wars
Civil wars that are fought over religion have tended to occur more in monotheistic than in polytheistic societies; one explanation is that the latter tend to be more "flexible" in terms of dogma, allowing for some latitude in belief. In Europe through the Middle Ages, the Christianity of the great bulk of the population was influenced by pagan tradition. With the great majority of the population illiterate, access to the Bible was limited and led to a significant amount of syncretism between Christian and pagan elements. With religion so loosely applied, it was rare for people to feel particularly oppressed by it. There were periodic appearances of heresies, such as that of the Albigensians, which led to violence, but historians tend to view these to be the product of peasant revolts rather than themselves motivators of a civil war.
As religions tended to become more rigidly defined and understood by their followers, inter-religious tensions generally increased. The rise of Islam witnessed a rash of uprisings against non-Islamic rulers soon after its appearance. Subsequent Islamic history has been marked by repeated civil conflicts, mostly stemming out of the Shi'ite-Sunni divide. In Europe the Protestant Reformation had a similar effect, sparking years of both civil and international wars of religion. Civil wars between Roman Catholicism and Protestantism consumed France in the Wars of Religion, the Netherlands during the Eighty Years' War, Germany during the Thirty Years' War, and more recently, The Troubles of Northern Ireland. Religious disputes among Protestant sects also played a role in the English Civil Wars, while official persecution of Catholics during the French Revolution spurred the Revolt in the Vendée. In China an attempt at religious revolution caused the bloodiest civil war of all time, the Taiping Rebellion.
A revolution is generally seen as a civil war fought over issues of ideology, over how power should be organized and distributed, not merely over which individuals hold it. The classic example of a revolution, and by some arguments the first is the French Revolution, which is seen to have pitted the middle class and urban poor of France against the aristocracy and monarchy. Some argue that revolutions are a modern continuation of the peasant revolts of the past. Unlike peasant revolts, however, revolutions are almost always led by members of the educated, but disaffected, middle class who then rally the large mass of the population to their cause. Others see ideology as merely replacing religion as a justification and motivation for violence that is fundamentally caused by socioeconomic factors. To be successful revolutions almost always require use of armed force and sometimes escalate to a civil war, such as in the Chinese Civil War. In some cases, such as the French and Russian Revolutions the revolutionaries succeed in gaining power through a quick coup or localized uprising, but a civil war results from counterrevolutionary forces organizing to crush the revolution.
One of the most common causes of civil wars, especially in the post-Cold War world has been separatist violence. Nationalism can be seen as similar to both a religion and an ideology as a justification for war rather than a root cause of conflict. All modern states attempt to hold a monopoly on internal military force. For separatist civil wars to break out thus either the national army must fracture along ethnic, religious, or national lines as happened in Yugoslavia; or more commonly a modern separatist conflict takes the form of asymmetrical warfare with separatists lightly armed and disorganized, but with the support of the local population such groups can be hard to defeat. This is the route taken by most liberation groups in colonies, as well as forces in areas such as Eritrea and Sri Lanka. Regional differences may be enhanced by differing economies, as in the American Civil War. National minorities are also often minorities and wars of religion may link closely into separatisty conflicts.
Coups d'état, in Spanish golpes de estado, are by definition quick blows to the top of a government that do not result in the widespread violence of a civil war. On occasion a failed coup, or one that is only half successful, can precipitate a civil war between factions. These wars often quickly try to pull in larger themes of ideology, nationalism, or religion to try to win supporters among the general population for a conflict that in essence is an intraelite competition for power.
Reasons for war
Almost every nation has minority groups, religious plurality, and ideological divisions, but not all plunge into civil war. Sociologists have long searched for what variables trigger civil wars. In the modern world most civil wars occur in nations that are poor, autocratic, and regionally divided. However, the United States was one of the wealthiest and most democratic countries in the world at the time of its bloody civil war.
Some models to explain the occurrence of civil wars stress the importance of change and transition. According to one such line of reasoning, the American Civil War was caused by the growing economic power of the North relative to the South; the Lebanese Civil War by the upsetting of the delicate demographic balance by the increase in the Shi'ite population; the English Civil War by the growing power of the middle class and merchants at the expense of the aristocracy.
Competition for resources and wealth within a society is seen as a frequent cause for civil wars, however economic gain is rarely the justification espoused by the participants. Marxist historians stress economic and class factors arguing that civil wars are caused by imperialist rulers battling each other for greater power, and using tools such as nationalism and religion to delude people into joining them. Also, recent evidence proved that the violence observed in civil war can come from spurious reasons.
Not only are the causes of civil wars widely studied and debated, but their persistence is also seen as an important issue. Many civil wars have proved especially intractable, dragging on for many decades. One contributing factor is that civil wars often become proxy wars for outside powers that fund their partisans and thus encourage further violence.
Research related to the democratic peace theory have studied civil wars and democracy. Research shows that the most democratic and the most authoritarian states have few civil wars, and intermediate regimes the most. The probability for a civil war is also increased by political change, regardless whether toward greater democracy or greater autocracy. Intermediate regimes continue to be the most prone to civil war, regardless of the time since the political change. In the long run, since intermediate regimes are less stable than autocracies, which in turn are less stable than democracies, durable democracy is the most probable end-point of the process of democratization . The fall of Communism and the increase in the number of democratic states were accompanied by a sudden and dramatic decline in total warfare, interstate wars, ethnic wars, revolutionary wars, and the number of refugees and displaced persons .