Summary/Abstract: This article aims to summarize the most significant schools and leading views (Conservative Realism, Liberal Revisionism, Rightist or Leftist Radicalism, Social Constructivism) in the contemporary European and American historiography as a common memory about the two world wars and their impact on 20th century international history. The leading issues that were subject of sharp disputes regarding both First and Second World Wars concerned the origins and causes, aims and strategies, national goals and coalition behavior, alternative outcomes and long term impacts over the postwar international system. The main distinctions among the military and civilian historiography, and among the political, social, and cultural historiography, are also clarified in this article. Beyond the historical approaches, attention was also paid to the political science, international relations, and security studies’ interpretations of the two world wars’ legacy. This paper also suggests a new comparative model of the main specifics of the three 20th century international systems in Europe, established in 1919, 1945, and 1991 in the modern and post-modern times.