Perhaps the most tangible expression of Hegel's ideas can be found in the various nationalist movements that erupted around the continent after the fall of Napoleon's empire. Hegel had argued that the nation-state should be the ultimate expression of Spirit, a metaphysical concept that essentially made God part of everything on Earth. Hegel also argued that society was progressing inexorably toward a time when reason would supplant religion as the dominant worldview. This idea was very popular, especially among positivists, and it was even embraced by many Social Darwinistic thinkers. Finally, Hegel's concept of a dialectic was embraced by many thinkers, notably Karl Marx, who was a "Young," or "Left" Hegelian as a student at the University of Berlin. Marx would later take the idea and "bring it down to earth" by placing it in terms of economic and social classes rather than ideas.