From Chechnya to Kashmir to the Basque region, secessionist movements remain a serious threat to international security. Despite the importance of this issue, the causes that bring about external military intervention in a secessionist war have not, until now, been adequately addressed. In this book, the author identifies the conditions that make international military intervention in a secessionist war more or less likely. South Asia, being fraught with secessionist movements, past and present - Bangladesh, Kashmir, the Tamils in Sri Lanka, and the movement for a Sikh state in Punjab - provides an ideal laboratory for the examination of this compelling issue.The author argues that a shift in the balance of power between a secessionist group and its central government will lead to a preventive war on the secessionists by the central government. In turn, a preventive war of this nature may lead to an alliance between the secessionist group and an external power. The stronger the alliance, the greater the chances of an international military intervention.Understanding the conditions under which secessionist movements expand, become secessionist wars, and invite international military intervention on behalf of the secessionists has strong policy implications. It can go a long way toward guiding policymakers who may want to mitigate or avoid these conditions in their states. The author views both states and secessionist groups as primary actors, and she examines both the distribution of power among states as well as the balance of power between central government and groups within states.