Collective Security Treaty Organization in the context of Inter-American Treaty of Reciprocal Assistance

The post–Cold War era is a period of history that follows the end of the Cold War, which represents history after the dissolution of the Soviet Union in December 1991. This period saw many former Soviet republics become sovereign states, as well as the introduction of market economies in Eastern Europe. This period also marked the United States becoming the world's sole superpower.

Relative to the Cold War, the period is characterized by stabilization and disarmament. Both the United States and Russia significantly reduced their nuclear stockpiles. Much of the former Eastern Bloc became democratic and was integrated into the world economy. In the first two decades of the period, NATO underwent three enlargements, and France reintegrated into the NATO command. Russia formed the Collective Security Treaty Organization to replace the dissolved Warsaw Pact, established a strategic partnership with China and several other countries, and entered the Shanghai Cooperation Organisation and BRICS alongside China, which is a rising power. Reacting to the rise of China, the United States began a gradual rebalancing of strategic forces to the Asia–Pacific region and out of Europe.

A neutral country is a sovereign state that is neutral towards belligerents in a specific war or holds itself as permanently neutral in all future conflicts (including avoiding entering into military alliances such as NATO, CSTO or the SCO). As a type of non-combatant status, nationals of neutral countries enjoy protection under the law of war from belligerent actions to a greater extent than other non-combatants such as enemy civilians and prisoners of war. Different countries interpret their neutrality differently: some, such as Costa Rica have demilitarized, while Switzerland holds to "armed neutrality", to deter aggression with a sizeable military, while barring itself from foreign deployment.

Not all neutral countries avoid any foreign deployment or alliances, as Austria and Ireland have active UN peacekeeping forces and a political alliance within the European Union. Sweden's traditional policy was not to participate in military alliances, with the intention of staying neutral in the case of war. Immediately before World War II, the Nordic countries stated their neutrality, but Sweden changed its position to that of non-belligerent at the start of the Winter War. Sweden would uphold its policy of neutrality until the 2022 Russian invasion of Ukraine. During the Cold War, former Yugoslavia claimed military and ideological neutrality from both the Western and Eastern Bloc, becoming a co-founder of the Non-Aligned Movement.