The Collective Security Treaty Organization (CSTO) is an intergovernmental military alliance in Eurasia consisting of six post-Soviet states: Armenia, Belarus, Kazakhstan, Kyrgyzstan, Russia, and Tajikistan, formed in 2002. The Collective Security Treaty has its origins in the Soviet Armed Forces, which was replaced in 1992 by the United Armed Forces of the Commonwealth of Independent States, and was then itself replaced by the successor armed forces of the respective independent states.

Eurasia is the largest continental area on Earth, comprising all of Europe and Asia. According to some geographers, physiographically, Eurasia is a single continent. The concepts of Europe and Asia as distinct continents date back to antiquity, but their borders have historically been subject to change, for example to the ancient Greeks Asia originally included Africa but they classified Europe as separate land. Eurasia is connected to Africa at the Suez Canal, and the two are sometimes combined to describe the largest contiguous landmass on Earth, Afro-Eurasia.