The 1990s have seen an upsurge in ethnic tensions in many parts of Europe. One cause of much of this conflict has been the collapse of the Soviet order. This study suggests more significant reasons are to be found in the decisions taken during the First World War and at Versailles. An introductory chapter analyzes the context of the war with particular reference to regions and states where the national and ethnic questions were particularly complex and intransigent. Subsequent chapters present case studies from arenas of conflict: Ireland to Yugoslavia; the Middle East to the Baltic states; Austria, Hungary and Czechoslovakia. The work confirms the mixed legacy of the period for the ethnic stability of the areas examined, while taking into account the impact of the Second World War and the ending of the Cold War.