'Legitimacy, peace, international law. A history of concepts and theory of human security' Security is a matter of course. The quest for security only springs from an awareness of insecurity. Security can consist in the ability to resist an attack, and in broader terms, freedom from fear, or in the perception of the predictability of the world. Security can therefore be understood in a narrower or wider sense, and can be linked to demonstrations of strength or to complex perceptions of the world. Kleinschmidt shows that the change in the concept of security was closely linked to perceptions of the public sphere and legitimacy. From the Middle Ages to the end of the 18th century, the analysis of the concept of security took place within the framework of theories of peace. It was not until the start of the 19th century that political theorists and practitioners began to limit the concept of security to the military. Between the 16th and 18th centuries, the aim of peace theory was to define the conditions for security. Only in the 19th century did security mutate into an element of war theory.