In examining the practice of socialist internationalism, this book has sought to combine three fields of historical scholarship (socialism, internationalism, and international politics) in the aim of contributing to each one. The contribution to the first area, socialism, is perhaps the most obvious. Contrary to numerous claims, socialist internationalism did not die in August 1914 but survived the outbreak of war and afterwards even flourished at times. Indeed, during the two post-war periods, European socialists worked closely together on a variety of pressing issues, endowing the policymaking of the British, French, and German parties with an important international dimension. This international dimension was never all-important: it rarely, if ever, trumped the domestic political and intra-party dimensions of policymaking. But its existence means that the international policies of any one socialist party cannot be fully understood in isolation from the policies of other parties. The practice of socialist internationalism was rarely easy: contention was present and sometimes rife. Equally pertinent, idealism could be in short supply. Often enough, European socialists instrumentalized internationalism for their own ends, whether it was Ramsay MacDonald with the Geneva Protocol during the 1920s or Guy Mollet, who hoped to discredit internal party critics of his Algerian policy during the 1950s. Nevertheless, the attempts to instrumentalize socialist internationalism underscore the latter’s significance. After all, such attempts would be inconceivable unless socialist internationalism meant something to European socialists....