By the 1750s a few regions of Western Europe were in the early stages of energy transition from plant fuels to fossil fuels and from animate prime movers to machines powered by combustion. Great powers of the past that continued to rely on traditional energy sources and on animate prime movers were swiftly left far behind: in aggregate terms China, with its large population, remained the world's largest economy until the 1880s. This chapter concentrates on just six universal measures for energy developments. They are energy density, power density, the maximum power of prime movers, the efficiency of energy conversions, the per capita consumption of useful energy, and, the maximum energies of weapons. The history of modern energy use make it clear how the combustion of fossil fuels and massive deployment of efficient prime movers created a world in which material comforts, private consumption, mobility, and the overall quality of life are so different from the pre-1750 era.