International Relations is one of the last branches of social science to have gained the status of an autonomous discipline. It was only officially accepted in academic circles in 1919, in the wake of the dramatic experience of the First World War, with the establishment of the first university teaching post at the University of Aberystwyth in Wales. Given that to a large extent it has progressed along a separate path from political philosophy and that this book is aimed at both political philosophers and international relations theorists, it may be useful to give a quick summary of the history of the discipline.