Since the industrialisation of Europe in the late nineteenth century, European armies have been able to trade firepower for manpower. The mass production of repeating weapons has made the battlefield more lethal, but it has also required fewer men proportionately to do the killing. As weapons have improved in quality, so they have reinforced the case against manpower in quantity. Technology was (and still can be) a force-multiplier.

This process did not initially result in smaller armies. Rather European states opted for both firepower and manpower: mass production enabled a large army to be equipped and supplied to a level and consistency that had defied the ambitions of less developed states. In August 1914 France mobilised eighty-two divisions and Germany eighty-seven, and each had almost three million men under arms. By late 1918 each of the three major allied armies on the western front (those of France, Britain and the United States, but not Belgium, which was cut off from its manpower pool) numbered in the region of two million men. These were conscript forces and represented the greatest numbers that their parent societies could bear. Although French and British divisions were smaller in manpower terms, and had fewer battalions than in 1914, they had increased their firepower ratio by the adoption of tanks, light machine guns, mortars and highly sophisticated artillery.