The Genocide Convention of 1948 was passed by the United Nations on 9 December 1948 in Paris. That date is a useful divide in any account of the phenomenon of genocide in the twentieth century, not only because of its formal acceptance in international law, subject to the ratification of two-thirds of the members of the United Nations. The date also separates two periods in the history of warfare. The first period, prior to 1948, may be termed the era of imperial and national war; the second, after 1948, may be termed the era of post-imperial warfare.