Peace operations were not invented by the United Nations after 1945, but developed gradually as part of the growing international relationship between the Great Powers in the nineteenth century. This essay looks at this evolution, and also tries to establish a working definition for peace operations (peace support operations) as the ‘umbrella term’ for missions ranging from unarmed civilian and military observers to fighting troops. Common elements are

• an international mandate,

• the multinational composition,

• the aim to either preserve or restore a status quo, or to supervise a peaceful transition from one status quo to another (as in the case of a former colony’s transition to independence),

• acting in the interest of the people of the guest country (and with the consent of the local legitimate government, if there is one), and

• adhesion to the principle of minimum damage (= measured force).