ABSTRACT Through a brief analysis of the reflections of some prestigious contemporary philosophers such as Norberto Bobbio, Mulford Quickert Sibley, Wilhelm Emil Mühlmann, Michael Allen Fox, David Cortright, Larry May, John Rawls, Eric Reitan, Johan Galtung and David Boersema, this essay reconstructs Russell's pacifist commitment during the First World War. This dramatic event represented a real watershed for his multifaceted and ingenious personality, leading to his new political and civil commitment. Through a series of articles and lectures, he fought against (...) militarism, was in favour of a world government and underlined the psychological causes of war. All this coincided in part with the outbreak of the Russian Revolution, the ideas of which he initially shared; at the time of the Leeds Convention, he believed that the March revolution would involve a complete political and economic change at the international level by removing the causes of war. It was not by chance that he decided to join the Independent Labour Party, a choice that marked his separation from the Liberals. Although the latter explored in depth different forms of pacifism, Russell implicitly recalled the formula ‘Pax enim non belli privatio’ by Baruch Spinoza, supporting a fundamental paradigm of the modern political theory. (shrink)