Collective security in the context of "Yalta Conference"

The Warsaw Pact (WP), formally the Treaty of Friendship, Cooperation and Mutual Assistance (TFCMA), was a collective defense treaty signed in Warsaw, Poland, between the Soviet Union and seven other Eastern Bloc socialist republics in Central and Eastern Europe in May 1955, during the Cold War. The term "Warsaw Pact" commonly refers to both the treaty itself and its resultant military alliance, the Warsaw Pact Organisation (WPO) (also known as ‘Warsaw Treaty Organization’ (‘WTO’)). The Warsaw Pact was the military complement to the Council for Mutual Economic Assistance (Comecon), the economic organization for the Eastern Bloc states.

Dominated by the Soviet Union, the Warsaw Pact was established as a balance of power or counterweight to the North Atlantic Treaty Organization (NATO) and the Western Bloc. There was no direct military confrontation between the two organizations; instead, the conflict was fought on an ideological basis and through proxy wars. Both NATO and the Warsaw Pact led to the expansion of military forces and their integration into the respective blocs. The Warsaw Pact's largest military engagement was the Warsaw Pact invasion of Czechoslovakia, one of its own member states, in August 1968. All member states participated except for Albania and Romania, resulting in Albania's withdrawal from the pact less than one month later. The pact began to unravel with the spread of the Revolutions of 1989 through the Eastern Bloc, beginning with the Solidarity movement in Poland, its electoral success in June 1989 and the Pan-European Picnic in August 1989.

The League of Nations (LN or LoN; French: Société des Nations [sɔsjete de nɑsjɔ̃], SdN) was the first worldwide intergovernmental organisation whose principal mission was to maintain world peace. It was founded on 10 January 1920 by the Paris Peace Conference that ended the First World War. The main organisation ceased operations on 18 April 1946 when many of its components were relocated into the new United Nations (UN) which was created in the aftermath of the Second World War.

The League's primary goals were stated in its eponymous Covenant. They included preventing wars through collective security and disarmament and settling international disputes through negotiation and arbitration. Its other concerns included labour conditions, just treatment of native inhabitants, human and drug trafficking, the arms trade, global health, prisoners of war, and protection of minorities in Europe. The Covenant of the League of Nations was signed on 28 June 1919 as Part I of the Treaty of Versailles, and it became effective with the rest of the Treaty on 10 January 1920. Australia was granted the right to participate as an autonomous member nation, marking the start of Australian independence on the global stage. The first meeting of the Council of the League took place on 16 January 1920, and the first meeting of the Assembly of the League took place on 15 November 1920. In 1919, U.S. president Woodrow Wilson won the Nobel Peace Prize for his role as the leading architect of the League. Despite this, he was ultimately unsuccessful in getting his country to join it.

The North Atlantic Treaty Organization (NATO /ˈneɪtoʊ/ NAY-toh; French: Organisation du traité de l'Atlantique Nord, OTAN), also called the North Atlantic Alliance, is an intergovernmental military alliance between 32 member states—30 in Europe and 2 in North America. Founded in the aftermath of World War II, NATO was established with the signing of the North Atlantic Treaty in 1949. The organization serves as a system of collective security, whereby its independent member states agree to mutual defence in response to an attack by any outside party. This is enshrined in Article 5 of the treaty, which states that an armed attack against one member shall be considered an attack against them all.

Throughout the Cold War, NATO's primary purpose was to deter and counter the threat posed by the Soviet Union and its satellite states, which formed the rival Warsaw Pact in 1955. Following the dissolution of the Soviet Union in 1991, the alliance adapted, conducting its first major military interventions in Bosnia and Herzegovina (1992–1995) and Yugoslavia (1999). Article 5 was invoked for the first and only time after the September 11 attacks, leading to the deployment of NATO troops to Afghanistan as part of the International Security Assistance Force (ISAF). The alliance has since been involved in a range of roles, including training in Iraq, intervention in Libya in 2011, and countering piracy.

In international relations, the liberal international order (LIO), also known as the rules-based order (RBO), consists of a set of global, rule-based, structured relationships based on political liberalism, economic liberalism and liberal internationalism since the late 1940s. More specifically, it entails international cooperation through multilateral institutions (like the United Nations, World Trade Organization and International Monetary Fund) and is constituted by human equality (freedom, rule of law and human rights), open markets, security cooperation, promotion of liberal democracy, and monetary cooperation. The order was established in the aftermath of World War II, led in large part by the United States.

The nature of the LIO, as well as its very existence, has been debated by scholars. The LIO has been credited with expanding free trade, increasing capital mobility, spreading democracy, promoting human rights, and collectively defending the Western world from the Soviet Union. The LIO facilitated unprecedented cooperation among the states of North America, Western Europe and Japan. Over time, the LIO facilitated the spread of economic liberalism to the rest of the world, as well as helped consolidate democracy in formerly fascist or communist countries.

NATO is a military alliance of thirty-two European and North American countries that constitutes a system of collective defense. The process of joining the alliance is governed by Article 10 of the North Atlantic Treaty, which allows for the invitation of "other European States" only and by subsequent agreements. Countries wishing to join must meet certain requirements and complete a multi-step process involving political dialogue and military integration. The accession process is overseen by the North Atlantic Council, NATO's governing body. NATO was formed in 1949 with twelve founding members and has added new members ten times. The first additions were Greece and Turkey in 1952. In May 1955, West Germany joined NATO, which was one of the conditions agreed to as part of the end of the country's occupation by France, the United Kingdom, and the United States, prompting the Soviet Union to form its own collective security alliance (commonly called the Warsaw Pact) later that month. Following the end of the Franco regime, newly democratic Spain chose to join NATO in 1982.

In 1990, negotiators reached an agreement that a reunified Germany would be in NATO under West Germany's existing membership. Following the dissolution of the Soviet Union in 1991, many former Warsaw Pact and post-Soviet states sought to join NATO. Poland, Hungary, and the Czech Republic became members in 1999, amid much debate within NATO itself. NATO then formalized the process of joining the organization with "Membership Action Plans", which aided the accession of seven Central and Eastern Europe countries shortly before the 2004 Istanbul summit: Bulgaria, Estonia, Latvia, Lithuania, Romania, Slovakia, and Slovenia. Two countries on the Adriatic Sea—Albania and Croatia—joined on 1 April 2009 before the 2009 Strasbourg–Kehl summit. The next member states to join NATO were Montenegro in June 2017, and North Macedonia in March 2020.

United Nations Command (UNC or UN Command) is the multinational military force established to support the Republic of Korea (South Korea) during and after the Korean War. It was the first attempt at collective security by the United Nations (UN) after the Charter of the United Nations was signed.

The UNC was established on 24 July 1950 following the United Nations Security Council's recognition, on 7 July, of North Korean aggression against South Korea. The motion passed because the Soviet Union, a close ally of North Korea and a member of the UN Security Council, was boycotting the UN at the time over its recognition of the Republic of China (Taiwan) rather than the People's Republic of China as 'China'. UN member states were called to provide assistance in repelling the North's invasion, with the UNC providing a cohesive command structure under which the disparate forces would operate. During the course of the war, 22 nations contributed military or medical personnel to UN Command; although the United States led the UNC and provided the bulk of its troops and funding, all participants formally fought under the auspices of the UN, with the operation classified as a "UN-led police action".

North Atlantic Treaty Organization (NATO) is an intergovernmental military alliance between 32 member states—30 in Europe and 2 in North America. Founded in the aftermath of World War II, NATO was established with the signing of the North Atlantic Treaty in 1949. The organization serves as a system of collective security, whereby its independent member states agree to mutual defence in response to an attack by any outside party. This is enshrined in Article 5 of the treaty, which states that an armed attack against one member shall be considered an attack against them all.

Throughout the Cold War, NATO's primary purpose was to deter and counter the threat posed by the Soviet Union and its satellite states, which formed the rival Warsaw Pact in 1955. Following the dissolution of the Soviet Union in 1991, the alliance adapted, conducting its first major military interventions in Bosnia and Herzegovina (1992–1995) and Yugoslavia (1999). Article 5 was invoked for the first and only time after the September 11 attacks, leading to the deployment of NATO troops to Afghanistan as part of the International Security Assistance Force (ISAF). The alliance has since been involved in a range of roles, including training in Iraq, intervention in Libya in 2011, and countering piracy.

The North Atlantic Treaty Organization (NATO) is an international military alliance consisting of 32 member states from Europe and North America. It was established at the signing of the North Atlantic Treaty on 4 April 1949. Of the 32 member countries, 30 are in Europe and two are in North America. Between 1994 and 1997, wider forums for regional cooperation between NATO and its neighbours were set up, including the Partnership for Peace, the Mediterranean Dialogue initiative, and the Euro-Atlantic Partnership Council.

All members have militaries, except for Iceland, which does not have a typical army (but it does have a coast guard and a small unit of civilian specialists for NATO operations). Three of NATO's members are nuclear weapons states: France, the United Kingdom, and the United States. NATO has 12 original founding member states. Three more members joined between 1952 and 1955, and a fourth joined in 1982. Since the end of the Cold War, NATO has added 16 more members from 1999 to 2024. Article 5 of the treaty states that if an armed attack occurs against one of the member states, it shall be considered an attack against all members, and other members shall assist the attacked member, with armed forces if necessary. Article 6 of the treaty limits the scope of Article 5 to the islands north of the Tropic of Cancer, the North American and European mainlands, the entirety of Turkey, and French Algeria, the last of which has been moot since July 1962. Thus, an attack on Hawaii, Puerto Rico, French Guiana, the Falkland Islands, Ceuta or Melilla, among other places, would not trigger an Article 5 response.