An idea is wrongly existing in the collective unconscious: that in which the first advocates of economic liberalism, British Classical economists, were convinced that trade was a factor for peace and that the spread of free trade would eradicate war. In recent times, F. Fukuyama’s theory on the "end of history" used this idea, among others. However the first Classical economists were much less definitive, on this issue, than is generally thought. In fact, neither Smith nor Ricardo nor Malthus said anything definitive about it. And Ricardian and Malthusian analyzes are so pessimistic about the long-term future of capitalism (reaching steady state, scarcity of food resources ...) that the idea of peace through free trade cannot be attributed to them. Only a current, one inherited from Jean-Baptiste Say, promised an end to war by spreading the liberal model (Frédéric Bastiat in France). This current, advocating radical measures (end of the army, unilateral disarmament) in the late 19th century, was accused of naivety, notably by J.M. Keynes. In the second half of the 19th century, while the free-trade is expanding and the world economy becomes "globalized", militarism is more prosperous than ever, particularly because of the colonial expeditions. This apparent contradiction will push some liberal economists to consider that international peace is not a given but can only result of a change in minds, through a proactive pacifist action. The role of liberal economists in "leagues for peace" and "international peace conferences”, very successful on the eve of the First World War, is decisive. In France, a liberal economist became a prominent figure of the European peace movement: Frédéric Passy, who recommends education as a means of fighting against the militaristic tendencies. But an even more famous economist has had a central role in the development of the peace movement: Léon Walras was in fact convinced that his scientific theory would strongly contribute to the establishment of the world peace. As Passy, Walras applied to the Nobel Peace Prize. However, only Passy, the Liberal who wanted to outlaw war, won the award in 1901.