Throughout modern history, war has been the major cause of a rising national debt. Most governments operate in fiscal balance during peacetime, financing their spending and investment by levying taxes and charging user fees. War emergencies push this balance into deficit – sometimes for defensive wars, sometimes for aggression. In Europe, parliamentary checks on government spending were designed to prevent ambitious rulers from waging war. This was Adam Smith’s great argument against public debts, and his urging that wars be financed on a pay-as-you-go basis. He wrote that if people felt the economic impact of war immediately – rather than postponing it by borrowing – they would be less likely to support military adventurism.