In advanced countries, the state’s capacity to govern sovereign territory within its borders is taken for granted. Yet as Lee shows in this pathbreaking book, in countries as diverse as Afghanistan, Indonesia, and Ukraine, large swaths of territory remain outside the state’s reach. Lee’s book provides the best study yet of how these ungoverned spaces have become important in international conflict. Powerful states engage in “foreign subversion” against their weaker rivals, often employing proxy forces such as provincial warlords or nonstate militias. These proxy groups attack representatives of the state in outlying areas, create rival administrative structures, and win the loyalty of locals at the expense of the national government. In this way, the aggressor state avoids the costs and risks of an overt war. Russia’s unofficial intervention in the Donbas region of Ukraine in 2014 is an iconic recent case of foreign subversion. But Lee also looks at other instances, including Malaysia’s subversive campaign against the Philippines in the late 1960s and 1970s and Thailand’s subversion of Vietnamese-occupied Cambodia in the 1980s. The book challenges one of the oldest insights in world politics, derived from the European state-building experience: that international conflict tends to strengthen the state.