The Ethics of Territorial Borders develops a distinctive line of argument, drawing on political theory and geography as well as international relations. It argues that although borders have played a role in ethical discussions about war, about intervention and about identity in international politics, these treat them as possessing derivative significance. Instead, this book critiques such an approach to argue for the ethical significance of borders themselves, pointing to their role in human diversity and the enduring appeal of territorial division. Territorial borders are a fundamental feature of international politics. However, for most accounts in international relations, territorial borders are taken for granted as the dividing lines between zones of sovereign control. Their location on the map may be highly controversial, hotly contested and the basis for some of human history's most violent and intractable conflicts.