It is widely acknowledged that a fair tax system is one of the most crucial foundations for any country to pursue stable development and human values. So how does a country accomplish tax fairness? This article argues that war finance and domestic economic inequality are two critical conditions. Historically, wars usually create opportunities for countries to enact progressive tax reforms. However, countries’ war finance choices are conditioned by domestic economic inequality. When inequality is low, the political leadership is more likely to secure a consensus of ‘equality of fiscal sacrifice’ between domestic wealthy elites and ordinary citizens. As a result, the leadership can more successfully enact progressive taxation, money creation and non-military spending cuts to pay for the war. Conversely, when inequality is high, the societal redistributive conflict could be more serious. Unable to strike a bargain of fiscal sacrifices without severe social instability, the leadership is expected to resort to a debt-financing strategy, which stifles tax progressivity and fairness. This article compares the United States’ war finance in the Korean and Vietnam Wars and finds supportive evidence. This article has important implications for the pursuits of tax fairness, democratic accountability, and the prospect for peace.