This book aims to explain the main highlights of the great twentieth century that is to say from the eve of the 1914-1918 war to the most recent news. From a strictly chronological point of view, we are entering the twenty first century with events that originated in the previous period. This is the case, for example, with the information and telecommunications sciences which currently support and structure the emergence of a planetary society. This globalization of flows and ideas also called globalization as the relation of man to the whole is certainly one of the major characteristics of the century which is beginning. But this new stage in the history of humanity is only possible thanks to the transformations, the ruptures of the past century.Around the world people are searching for the hidden realities which are debatable, disputed and insoluble masteries. So we have to look theses topics in depth.