An original conceptual approach to the study of war, attempting to capture the entire phenomenon of military adaptation—whether strategic, institutional or in the field. The unravelling of the post-Cold War order has intensified geopolitical tensions, driving a global increase in defence spending. Most military organisations are engaged in a process of drastic transformation, trying to scale their activities, learn from contemporary battlefields, and improve readiness. Yet armed forces engaged in such reforms must solve a major dilemma: how to adapt to an uncertain future without losing their current identity, coherence or operational effectiveness. In this incisive and timely study, Olivier Schmitt explores how modern militaries adapt, or fail to adapt, to evolving threats, technologies and political constraints. Drawing on global case-studies--from the trenches of Ukraine to the halls of the People's Liberation Army leadership--he investigates how social expectations, political constraints and organisational cultures collide in the worldwide quest to reform the military. Essential reading for defence professionals, policymakers and scholars of international security, Preparing for War equips readers with the tools to grasp not only the 'how' but the 'why' behind military transformation. In an era of rising defence budgets and shrinking certainties, this book delivers crucial insights into the future of war--and the institutions that must be ready for it.