The most obvious impact of the nation state, as compared to its non-national predecessors, is the creation of a uniform national culture, through state policy. The model of the nation state implies that its population constitutes a nation, united by a common descent, a common language and many forms of shared culture. When the implied unity was absent, the nation state often tried to create it. It promoted a uniform national language, through language policy. The creation of national systems of compulsory primary education and a relatively uniform curriculum in secondary schools, was the most effective instrument in the spread of the national languages. The schools also taught the national history, often in a propagandistic and mythologised version, and (especially during conflicts) some nation states still teach this kind of history.