 Wars destroy lives and environments. In the eight years following the Iraq invasion in 2003, half a million deaths were either directly or indirectly caused by the war (Hagopian et al. 2013). Direct casualties from the Second World War numbered over 60 million, about 3 per cent of the world’s population. War’s environmental costs are less commonly researched, but are obviously also extraordinary (Austin and Bruch 2000). Armed forces use fuels in Olympian quantities: in the years from 2000–2013, the US Department of Defense accounted for around 80% of US federal government energy usage, between 0.75 and 1 quadrillion BTUs per year—a little less than all the energy use that year in Denmark and Bulgaria, a little more than Slovakia and Serbia (Energy Information Administration 2015a,b). They also directly and indirectly destroy habitats and natural resources—consider, for example, the Gulf war oil spill (El-Baz and Makharita 1994). For both our planet and its inhabitants, wars are truly among the very worst things we can do.