The biggest restriction of this new industrial era was no longer muscle, water, or wind—or even energy in general—but instead capital. Everything about this new era—whether it be railroads or highways or assembly lines or skyscrapers or battleships—was, well, new. It replaced the infrastructure of the previous millennia with something lighter, stronger, faster, better . . . and that had to be built up from scratch. That required money, and lots of it. The demands of industrialized infrastructure necessitated new methods of mobilizing capital: capitalism, communism, and fascism all emerged.
