Geoffrey Blainey has long been one of Australia's most prominent, and at times controversial historians. Apart from his usual focus on Australian history, his primary work concerning international politics has been his book 'The Causes of War', making him one of the more notable Australian contributors to issues of war and peace in the field of international relations. His theory on the causes of war is based on an implicit rational actor model of perceptions of military power. His hypothesis is: When two sides disagree on their relative strength, war is likely. When they agree, peace is likely. With case studies on the wars in Nagorno-Karabakh and Sierra Leone, this book considers whether Blainey's hypothesis on war, which was designed to analyse international wars, remains applicable to contemporary internal wars. Blainey's ambition was to come up with a general theory on why wars begin and conclude. Before claiming that his theory is truly comprehensive, and still relevant, it needs to be tested against the dominant form of warfare today; internal, or intrastate wars.