Published under the suspices of the Institute of Human Relations, this is an inquiry into the psychological foundation of war and peace, which May believes to be the result of social conditioning. He surveys war as the product of man's instincts, war as a part of social evolution, etc. and then presents his theory that war is the product of learning. He analyzes behaviour patterns in the individual, -- learning to fight, to hate, to fear, to escape, to love, to defend, to follow leaders. He then discusses habits, attitudes in group behaviour, mass movements which are aggressive or defensive. He concludes that psychological conditions of peace can be achieved first by controlling group aggression, second by creating solidarity. Theory and research.