Why do big, powerful countries with strong militaries sometimes lose wars to small countries with weak ones?

That is the question being asked by a researcher at the University of Georgia School of Public and International Affairs. Patricia Sullivan analysed 122 military interventions since the second world war in which the US, the UK, the Soviet Union, Russia, China or France fought a weaker adversary. The more powerful country failed to achieve its objectives 39 per cent of the time.