Marx and Engels famously wrote: "Workers of the world unite. You have nothing to lose but your chains." They should have added: "And if you don't pull together, a lot of you will die in bloody wars." For if the workers of Britain and Germany and of all the other countries had heeded Marx and Engel's call and refused to fight each other, then there could have been no war in 1914. But there was such a war because Marx and Engels failed to see, in the Great Powers game that was building up, that lethal popular nationalisms would erupt, that workers in each country would rally round their own flags, that nations would trump class, and that war would trump peace.