The Collective Security Treaty Organization is a military alliance that currently has 6 members: Armenia, Belarus, Kazakhstan, Kyrgyzstan, Russia, and Tajikistan, which regularly conduct joint exercises. CSTO members cannot join any other military alliance or host foreign military on their soil unless all other member countries agree. This prevents, for example, the U.S. from establishing a military base in Tajikistan without Russia's consent.
Similar to NATO's Article 5, Article 4 of the CSTO treaty states that an aggression against one member is considered an aggression against all. This mutual defense clause was successfully triggered during the protests in Kazakhstan in early 2022, even though there was no direct attack on a member state. The CSTO has also refused calls from Kyrgyzstan and Armenia to trigger Article 4 before and failed to prevent clashes between its member states Kyrgyzstan and Tajikistan.
