This book assesses the nature and broader significance of warfare in the mountains of classical Greece. Based on detailed reconstructions of four unconventional military encounters, the book argues that the upland Greeks of the classical mainland developed defensive strategies to guard against external aggression. These strategies enabled wide-scale, sophisticated actions in response to invasions, but they did not require the direction of a central, federal government. The book brings these strategies to the forefront by driving ancient Greek military history and ancient Greek scholarship “beyond the polis” into dialogue with each other. As it contends, beyond-the-polis scholarship has done much to expand and refine our understanding of the ancient Greek world, but it has overemphasized the importance of political institutions in emergent federal states and has yet to treat warfare involving upland Greeks systematically or in depth. In contrast, the book scrutinizes the sociopolitical roots of warfare from beyond the polis, which are often neglected in military histories of the Greek city-state. By focusing on the significance of warfare vis-à-vis the sociopolitical development of upland polities, the book shows that although the more powerful states of the classical Greek world were dismissive or ignorant of the military capabilities of upland Greeks, the reverse was not the case. The Phocians, Aetolians, Acarnanians, and Arcadians in circa 490–362 BCE were well aware of the arrogant attitudes of their aggressive neighbors, and as highly efficient political entities, they exploited these attitudes to great effect.