Clash of Civilizations
In his 1993 book "Clash of Civilizations and the Remaking of World Order" (published by the Council on Foreign Relations), Samuel P. Huntington hypothesizes that "the fundamental source of conflict in this new world [of politics] will not be primarily ideological or primarily economic. The great divisions among humankind and the dominating source of conflict will be cultural. Nation states will remain the most powerful actors in world affairs, but the principal conflicts of global politics will occur between nations and groups of different civilizations. The Clash of Civilizations will dominate global politics. The fault lines between civilizations will be the battle lines of the future." 
Huntington says that the reason "why civilizations will clash will be increasingly important in the future, and the world will be shaped in large measure by the interactions among seven or eight major civilizations. These include Western, Confucian, Japanese, Islamic, Hindu, Slavic-Orthodox, Latin American and possibly African civilization. The most important conflicts of the future will occur along the cultural fault lines separating these civilizations from one another." 
He offers six reasons for why this is so: 
- "First, differences among civilizations are not only real; they are basic. Civilizations are differentiated from each other by history, language, culture, tradition and, most important, religion."
- "Second, the world is becoming a smaller place."
- "Third, the processes of economic modernization and social change throughout the world are separating people from longstanding local identities. They also weaken the nation state as a source of identity."
- "Fourth, the growth of civilization-consciousness is enhanced by the dual role of the West. On the one hand, the West is at a peak of power. At the same time, however, and perhaps as a result, a return to the roots phenomenon is occurring among non-Western civilizations."
- "Fifth, cultural characteristics and differences are less mutable and hence less easily compromised and resolved than political and economic ones. In the former Soviet Union, communists can become democrats, the rich can become poor and the poor rich, but Russians cannot become Estonians and Azeris cannot become Armenians."
- "Sixth, economic regionalism is increasing."
"As people define their identity in ethnic and religious terms, they are likely to see an 'us' versus 'them' relation existing between themselves and people of different ethnicity or religion." 
"The clash of civilizations thus occurs at two levels. At the micro-level, adjacent groups along the fault lines between civilizations struggle, often violently, over the control of territory and each other. At the macro-level, states from different civilizations compete for relative military and economic power, struggle over the control of international institutions and third parties, and competitively promote their particular political and religious values." 
A section of the first chapter is available online at The New Era in World Politics, Washington Post.