A cultural phenomenon
One school of thought says that civilisation is a cultural identity which represents the broadest level of identification in which an invididual intensely identifies, broader than family, tribe, hometown, nation, or region. Civilizations are usually tied to religion or some other belief system.
The concept of civilization is central to the historical theories of Arnold J. Toynbee who described history as the process of the rise and decline of civilizations, of which he identified 26. It is also central to the political beliefs of Samuel P. Huntington who argues that the defining characteristic of the 21st century will be the interaction and conflict between civilizations.
The concept of empire overlaps with that of "civilisation", so the empirical description of the 500-year old Western empire by Noam Chomsky and the more theoretical analysis by Negri and Hardt constitute other contemporary analyses of civilisations.
25 major civilizations in Human History