Most contemporary students and proponents of cosmopolitanism would identify it as a philosophy of peace, based on mutual tolerance, recognition, dialogue and commitment to global justice. This chapter argues that, though true, this account of cosmopolitanism is historically incomplete and conceptually truncated. It shows how such a pacific conception of cosmopolitanism had to be positively argued for in the Enlightenment against currents of cosmopolitanism reaching back to the Stoics that presented it as conflictual and conflicted. In particular, it argues that there has been a long and complex relationship between conceptions of cosmopolitanism and ideas of civil war from ancient Rome to our own age of “Global Civil War.” It presents the darker side of cosmopolitanism as a philosophy of conflict as well as compromise, of war as well as peace and of civil war as well as of civilisation and civility.