Norrie MacQueen 
Peacekeeping and the International System [PDF ebook] 

A comprehensive, clearly presented and accessible text covering the totality of the peacekeeping experience since the early twentieth century. This is essential reading for all undergraduates on politics, international relations and contemporary history programmes. It is also an excellent resource for taught postgraduate courses in these subject areas.The narrative is primarily chronological; key themes such as legality and 'collective security’ are traced throughout. The chronology is based on the key periods in the development of peacekeeping, marking stages in the evolution of the concept determined by changes in the nature of the international system over the past six decades.