Nationalism, like many other terms in social science, such as 'democracy', 'revolution', 'liberalism', or 'socialism', is a broad one, and is used to describe two quite distinct things: a Political doctrine or ideology, i.e. a set of political principles that movements and individuals espouse, and a social and political movement, a tendency that has, over the whole globe and for the past two centuries, affected all societies and transformed their politics. It is important, in this as in the other case, to keep discussion of the two separate.