The original root of the metaphysical and moral beliefs of the currently dominant culture lies in the crisis of the European sciences of the twentieth century’s first decades, an expression of a nihilism whose germ can be found in positivism and whose fruit in postmodernism. The article proposes an investigation in this sense, analyzing – within the space limitations allowed here – the evolution of philosophical thought, of the mathematical, physical and natural sciences, of literature and of the arts in the West from 1850 to 1930 in terms of history of ideas, science and culture, providing a clarification of the relationship between the loss of a unitary and rationally founded vision of knowledge and the consequent existential bewilderment characterizing the European humanity of the period. The conclusions reveal the origin of the fundamental assumptions defining the thought subsoil of today’s Western civilization, specifying the centrality of the problem of knowledge fragmentation not only on a theoretical and scientific level, but also with regard to its ethical and political consequences.