Peace is not simply the absence of war but a positive condition, a state of affairs in which war is impossible. This necessarily implies that war is not an inevitable part of the human condition but has specific causes the removal of which would then lead to a state of general peace. The notion of peace has been a central one for western political philosophy from the Middle Ages onwards and the twin questions of whether peace is possible and, if so, how it may be brought about are important for all ideologies. In more recent times this question has become prominent because of the threat of nuclear war and the rise in most western societies of an organized 'peace movement'. The current attitudes of most conservatives and classical liberals are strongly influenced by contemporary political disputes and the partisan identification of 'peace theory' with the political left. This obscures a more complex history.