This book asks why weaker powers so often engage in wars against stronger opponents. It examines six cases where this occurred in this century, including the Japanese attack on Pearl Harbor in 1941, and the Argentine invasion of the Falkland Islands in 1982. The key argument of deterrence theory is that the military superiority of a relatively strong power, coupled with a credible retaliatory threat, will prevent attack by challengers. This book seriously challenges this assumption, and has wide implications for the study of war, deterrence, diplomacy and strategy.