Like the UN as a whole, the Security Council was created following World War II to address the failings of a previous international organization, the League of Nations, in maintaining world peace. In its early decades, the Security Council was largely paralyzed by the Cold War division between the US and USSR and their respective allies, though it authorized interventions in the Korean War and the Congo Crisis and peacekeeping missions in the Suez Crisis, Cyprus, and West New Guinea. With the collapse of the Soviet Union, UN peacekeeping efforts increased dramatically in scale, and the Security Council authorized major military and peacekeeping missions in Kuwait, Namibia, Cambodia, Bosnia, Rwanda, Somalia, Sudan, and the Democratic Republic of Congo.
The Security Council consists of fifteen members. The great powers that were the victors of World War II—the Soviet Union (now represented by the Russian Federation), the United Kingdom, France, the Republic of China (now represented by the People's Republic of China), and the United States—serve as the body's five permanent members. These permanent members can veto any substantive Security Council resolution, including those on the admission of new member states or candidates for Secretary-General. The Security Council also has 10 non-permanent members, elected on a regional basis to serve two-year terms. The body's presidency rotates monthly among its members.
Security Council resolutions are typically enforced by UN peacekeepers, military forces voluntarily provided by member states and funded independently of the main UN budget. As of 2016, 103,510 peacekeepers and 16,471 civilians were deployed on sixteen peacekeeping operations and one special political mission.
In the century prior to the UN's creation, several international treaty organizations and conferences had been formed to regulate conflicts between nations, such as the International Committee of the Red Cross and the Hague Conventions of 1899 and 1907. Following the catastrophic loss of life in World War I, the Paris Peace Conference established the League of Nations to maintain harmony between the nations. This organization successfully resolved some territorial disputes and created international structures for areas such as postal mail, aviation, and opium control, some of which would later be absorbed into the UN. However, the League lacked representation for colonial peoples (then half the world's population) and significant participation from several major powers, including the US, USSR, Germany, and Japan; it failed to act against the 1931 Japanese invasion of Manchuria, the Second Italo-Ethiopian War in 1935, the 1937 Japanese occupation of China, and Nazi expansions under Adolf Hitler that escalated into World War II.
The earliest concrete plan for a new world organization began under the aegis of the US State Department in 1939. Roosevelt first coined the term United Nations to describe the Allied countries."On New Year’s Day 1942, President Roosevelt, Prime Minister Churchill, Maxim Litvinov, of the USSR, and T. V. Soong, of China, signed a short document which later came to be known as the United Nations Declaration and the next day the representatives of twenty-two other nations added their signatures." The term United Nations was first officially used when 26 governments signed this Declaration. By 1 March 1945, 21 additional states had signed. "Four Policemen" was coined to refer to the four major Allied countries: the United States, the United Kingdom, the Soviet Union, and China. and became the foundation of an executive branch of the United Nations, the Security Council.