For millions of people The Communist Manifesto has served as an essential text, greatly affecting their ways of life. It has influenced nation-building, affected social and economic policies, and played a very important role in world politics as nations drew alliances during the Cold War. Vast amounts of commentary have been produced by both pro-communist and anti-communist scholars and critics. Marx and Engels themselves contributed to the debates through their numerous revisions of the preface to The Communist Manifesto. Upon the text's seventy-fifth anniversary, Algernon Lee explored the European influences on Marx and Engels as they were formulating their ideas. With The Communist Manifesto's one hundredth birthday, Paul M. Sweezy and Leo Huberman reexamined the text's history and its international significance. Some critics have explored the authors' own lives and education in an effort to elucidate The Communist Manifesto. Others have detected a wide and diverse range of influences on the work, including Romanticism, French materialist philosophy, millenarianism, Darwinism, and Gothic melodrama. Rhetorical analyses of the text have been conducted, as have economic, political, cultural, and philosophical readings. Since the collapse of the Soviet Union The Communist Manifesto has increasingly been examined as an historical document, as the product of a particular historical moment. As one of the most important secular documents in human history, however, The Communist Manifesto remains assured of its place in the literary canon, and the philosophy it espouses retains a certain force in contemporary social, economic, and political thought.