The conception of "French" culture however poses certain difficulties and presupposes a series of assumptions about what precisely the expression "French" means. Whereas American culture posits the notion of the "melting-pot" and cultural diversity, the expression "French culture" tends to refer implicitly to a specific geographical entity (as, say, "metropolitan France", generally excluding its overseas departments) or to a specific historico-sociological group defined by ethnicity, language, religion and geography. The realities of "Frenchness" however, are extremely complicated. Even before the late nineteenth century, "metropolitan France" was largely a patchwork of local customs and regional differences that the unifying aims of the Ancien Régime and the French Revolution had only begun to work against, and today's France remains a nation of numerous indigenous and foreign languages, of multiple ethnicities and religions, and of regional diversity that includes French citizens in Corsica, Guadeloupe, Martinique and elsewhere around the globe.