This study presents an interpretation of Hannah Arendt's reflection on man as a being of the world as well as the most general worldly conditions of human existence: natality, mortality, planet Earth, organic life, worldliness and plurality. By examining the untold totalitarian deworldlization, it aims at analyzing as to what extent Arendt critically reconsidered the pre-modern and modern acosmism, distinctly expressed both in the conceptual scenario of traditional political philosophy and in the history of hierarchical assortment of man's most active and basic engagements (labor, work and action) and not active (thinking) in the world. The term acosmism literally means a denial of the cosmos (mundus, in Latin), a degradation of everything which connects the human existence to the world common, or yet, a lack of balance in the full foundation and preservation of the world, and above all, of the public side of the world. Therefore, this study rebuilds what according to Arendt were the crucial factors that led to the world collapse which resulted in this shallow crowd dominated by terror and indoctrination in the ideology of totalitarianism in the 20th century. The totalitarian regimes broke the line of Occidental History, pointing out the coming of a dim era in relation to the traditional philosophic legacy and brightening up the trances of our times still so much current in modern societies' passage to the 21st century.