This chapter introduces the study of the law of armed conflict by considering the nature and legality of war. The treatment of Napoleon served as a precedent for the policy adopted by the principal Allied and Associated Powers at the end of World War I when considering the treatment to be accorded to those responsible as authors of that war. A more definite attempt to render the war illegal is to be found in the Covenant of the League of Nations. The United States was not a member of the League, but by virtue of being among the victors in 1918 was an important power whose views could not be ignored. In 1946 the General Assembly at its first session adopted a resolution affirming 'the principles of international law recognised by the Charter of the Nuremberg Tribunal and the judgment of the Tribunal'.