The article is a survey of some of numerous paradoxes connected with the history of the notion 'nation.' In its contemporary meaning, this notion transferred, in a relatively short time, from a vague idea known to some eccentric thinkers into an indispensable component of the identity of each and every inhabitant of our continent. In a relatively short period the people inhabiting Europe were first classified according to many flexible criteria (such as residence, belonging to particular social strata, confessed religion, respected authority, language spoken, etc.), and later divided into multimillion national communities, apparently existing from time immemorial and separated by eternal barriers of contradictory national interests. Attempts to cross these barriers made by a human being - i.e., transferring from one community to another - are now treated as a rejection and betrayal of one's own identity. The article tries to present how such a violent change could have happened, to what extent national ideology was a by-product of economic and social processes initiated in Europe as early as the Middle Ages, and to what degree this ideology was a stimulus for these processes, and, last but not least, to what extent this ideology contributed to the creation of the contemporary shape of the world, in which western civilization managed to win primacy and maintain it till the present day, and, moreover, impose its standards on other cultures - among them the dogma about a necessary division into rival nations, which is apparently an effect of human nature itself.