The Collective Security Treaty Organization (CSTO; Russian: Организация Договора о Коллективной Безопасности, Organizatsiya Dogovora o Kollektivnoy Bezopasnosti, ODKB) is an intergovernmental military alliance that was signed on 15 May 1992. In 1992, six post-Soviet states belonging to the Commonwealth of Independent States—Russia, Armenia, Kazakhstan, Kyrgyzstan, Tajikistan, and Uzbekistan—signed the Collective Security Treaty (also referred to as the "Tashkent Pact" or "Tashkent Treaty"). Three other post-Soviet states—Azerbaijan, Belarus, and Georgia—signed the next year and the treaty took effect in 1994. Five years later, six of the nine—all but Azerbaijan, Georgia, and Uzbekistan—agreed to renew the treaty for five more years, and in 2002 those six agreed to create the Collective Security Treaty Organization as a military alliance. Uzbekistan rejoined the CSTO in 2006 but withdrew in 2012.
Nikolai Bordyuzha was appointed secretary general of the new organization. On 23 June 2006, Uzbekistan became a full participant in the CSTO; and its membership was ratified by the Uzbek parliament on 28 March 2008. It suspended its membership in 2012. The CSTO is an observer organization at the United Nations General Assembly.
Collective security can be understood as a security arrangement, political, regional, or global, in which each state in the system accepts that the security of one is the concern of all, and therefore commits to a collective response to threats to, and breaches to peace. Collective security is more ambitious than systems of alliance security or collective defense in that it seeks to encompass the totality of states within a region or indeed globally, and to address a wide range of possible threats. While collective security is an idea with a long history, its implementation in practice has proved problematic. Several prerequisites have to be met for it to have a chance of working.
Collective security is one of the most promising approaches for peace and a valuable device for power management on an international scale. Cardinal Richelieu proposed a scheme for collective security in 1629, which was partially reflected in the 1648 Peace of Westphalia. In the eighteenth century many proposals were made for collective security arrangements, especially in Europe.