Exploring reason of state in a global monarchy, The Power of Necessity examines how thinkers and agents in the Spanish monarchy navigated the tension between political pragmatism and moral-religious principle. This tension lies at the very heart of Counter-Reformation reason of state. Nowhere was the need for pragmatic state management greater than in the overstretched Spanish Empire of the seventeenth century. However, pragmatic politics were problematic for a Catholic monarchy steeped in ideals of justice and divine justifications of power and kingship. Presenting a broad cast of characters from across Europe, and uniting published sources with a wide range of archival material, Lisa Kattenberg shows how non-canonical thinkers and agents confronted the political-moral dilemmas of their age by creatively employing the legitimising power of necessity. Pioneering new ways of bridging the persistent gap between theory and practice in the history of political thought, she casts fresh light on the struggle to preserve the monarchy in a modernising world.