Leaders weighing the merits of war must assess what can be achieved with force and at what cost. Their assessments dictate which peaceful settlements they prefer to fighting. This project explores (1) how leaders form these assessments and (2) when these assessments promote war or peace. Addressing these issues illuminates the critical and often neglected role that advisers and their affiliated bureaucracies play in providing information to leaders who must operate under intense time constraints. The book thus expands the investigative scope beyond leaders, bringing advisers and bureaucracies to the fore. Stressing the importance of who is in the room with the leader reveals a common flaw in assessment processes. Leaders often marginalize advisers with substantive expertise in an adversary’s political, as opposed to military, attributes. This marginalization produces informational blindspots on political traits—such as adversary resolve or the likely post-conflict political landscape. Blindspots breed misplaced certainty. Ignorant yet certain, leaders blunder into war.

In support of the argument, the project marshals evidence from case studies as well as analyses employing new measures of advisory input, certainty, and hawkishness based on a corpus of security documents from US Cold War crises.

Analyzing assessment processes and embedding them in a strategic account of international crises yields new insights. It reveals limits to when certainty fosters peace and enhances welfare. Additionally, it highlights the informational role of advisers and their associated bureaucracies. A division of labor in bureaucratic responsibilities causes advisers to develop specialized expertise. Information, not policy prescriptions, is the salient cleavage among bureaucracies in matters of war and peace. Sidelining those with expertise in an adversary’s political characteristics impairs assessments and helps account for numerous foreign policy fiascos since the Second World War.