War, as Clausewitz reminds, is the most uncertain of human political and social activities. It also imposes burdens. In an alliance among states for the promotion of collective defense or security, such as the North Atlantic Treaty Organization (NATO), burdens have to be shared. This study looks at the experience of the United States and other member states of NATO in four situations of multinational military intervention – Lebanon, the Persian Gulf, the Balkans, and South Asia – and considers the implications of nuclear arms reductions and nonproliferation for the US and NATO. Each case study represents an important period in the distribution of power, interest, and values, amounting to more than a sequential consideration of incidents of military intervention and/or conflict prevention. These politico-military challenges include a major coalition war, a traditional peacekeeping operation, an exercise in peace enforcement, and a conflict that combines counter-insurgency and counter-terrorism with stability and security operations.