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 18th–19th 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 also in America.