Europe's NATO members have pledged 3.5% of GDP to rearmament. The political argument is already about which social programmes will be sacrificed to pay for this, when the government chooses guns instead of butter. What does history tell us about what politicians will do? Christoph Trebesch and Johannes Marzian spent four years assembling the Global Budget Database: 150 years of primary government budget documents from 20 countries, with 116 identified military spending booms in peace and war.