ORBIS

Alliance · Military

CSTO

Collective Security Treaty Organization

The Collective Security Treaty Organization is a military alliance led by Russia, with five other former Soviet republics: Belarus, Kazakhstan, Kyrgyzstan, Tajikistan and Armenia. Like NATO, its treaty treats an attack on one member as an attack on all. Its headquarters are in Moscow. It has sent troops only once, to Kazakhstan in January 2022. Armenia froze its membership in 2024.

Updated October 2026 · Members and treaty text from the CSTO, spending from SIPRI

Leaders sit around a large round table in a hall in Bishkek, in front of two rows of flags of the CSTO's six members and of the CSTO itself
The CSTO summit in Bishkek, Kyrgyzstan, November 2025. Armenia's flag is there, but its prime minister stayed away. Photo: Presidential Executive Office of Russia (kremlin.ru), CC BY 4.0.
Members
6
Armenia froze its part in 2024
Treaty signed
1992
In Tashkent, Uzbekistan
Headquarters
Moscow
Russia chairs in 2026
Economy
$3.1tn
85% of it Russia's, 2025
Secretary General
Taalatbek Masadykov
Since January 2026

Which countries are in the CSTO?

The CSTO has six members, all former Soviet republics: Russia, Belarus, Kazakhstan, Kyrgyzstan, Tajikistan and Armenia. Six countries signed the treaty in Tashkent on May 15, 1992: Russia, Armenia, Kazakhstan, Kyrgyzstan, Tajikistan and Uzbekistan. Azerbaijan, Georgia and Belarus joined in 1993. In April 1999 Azerbaijan, Georgia and Uzbekistan refused to extend it. Azerbaijan objected to Russia's military support for Armenia over Karabakh. Georgia objected to Russia's backing of Abkhazia and South Ossetia. Uzbekistan returned in 2006 and suspended its membership in 2012.

The charter, signed in Chișinău on October 7, 2002, created a formal organization headquartered in Moscow. Russia has military bases in three members: Tajikistan, Kyrgyzstan and Armenia. The 201st base in Tajikistan is Russia's largest base abroad. From 2003 to 2014 Kyrgyzstan hosted both Russia's Kant air base and a US air base at Manas, about 30 km apart.

Map of Russia west of Lake Baikal, Central Asia and the Caucasus. The CSTO members are blue: Russia, Belarus, Kazakhstan, Kyrgyzstan and Tajikistan. Armenia, which froze its membership in 2024, is dark blue. Azerbaijan, Georgia and Uzbekistan, which left, are rust.
  • Member
  • Froze its membership
  • Left
  • Not a member

How the CSTO grew and shrank

Countries that joined in each year, and the total after

  1. ArmeniaKazakhstanKyrgyzstanRussiaTajikistanUzbekistan19926 founders
  2. AzerbaijanBelarusGeorgia19939
  3. Azerbaijan leftGeorgia leftUzbekistan left19996, Azerbaijan, Georgia and Uzbekistan out
  4. Uzbekistan20067
  5. Uzbekistan left20126, Uzbekistan out

All 6 members and the year each joined

  • Armenia1992
  • Belarus1993
  • Kazakhstan1992
  • Kyrgyzstan1992
  • Russia1992
  • Tajikistan1992

What does the CSTO promise its members?

Article 4 of the treaty says aggression against one member counts as aggression against all. The others must provide help, including military help. Since 2010 help comes only if the attacked member asks. The CSTO's text says the others "shall immediately provide" help. NATO's Article 5 lets each ally take the action it "deems necessary." NATO's promise covers Europe and North America. The CSTO's promise has no geographic limit.

All decisions need consensus, so any one member can block a response. The article has been used to send troops once, to Kazakhstan in January 2022. Armenia invoked it in September 2022 after Azerbaijan attacked its territory. The CSTO sent no troops.

…all the other member states, at the request of that member state, shall immediately provide it with the necessary assistance, including military assistance…

Article 4, Collective Security Treaty, 1992, as amended in 2010 (translated from the Russian)
Troops sent
Once, January 2022

To Kazakhstan at President Tokayev's request. 2,030 troops, mostly Russian, from January 6 to 19, 2022.

Rapid reaction force
About 20,000

Set up in 2009 from each member's military and special forces units.

When has the CSTO sent troops?

The CSTO has sent troops once. In January 2022 protests spread across Kazakhstan after the price of car fuel jumped from about 80 to 120 tenge a liter. On January 5 President Kassym-Jomart Tokayev asked the CSTO for help and called the protesters "terrorist groups" trained abroad. On January 7 he ordered his forces to shoot to kill without warning. The CSTO's 2,030 troops guarded airports, military depots and other sites. They left on January 19. Kazakhstan's prosecutors counted 238 dead.

Armenia's prime minister, Nikol Pashinyan, chaired the CSTO that year and announced the deployment. Armenia sent about 100 soldiers. Eight months later Armenia asked for help after Azerbaijan attacked its territory. The CSTO sent only a fact-finding mission.

  • KazakhstanTroops sent

    2,030 troops, mostly Russian, guarded airports and other sites during deadly unrest in January 2022. They left after 13 days.

  • KyrgyzstanNo troops

    Ethnic violence around Osh in June 2010 killed about 470 people. Kyrgyzstan's interim leader asked Russia for peacekeepers. The CSTO decided not to send troops.

  • ArmeniaNo troops

    In September 2022 Azerbaijan attacked inside Armenia. Armenia invoked Article 4. The CSTO sent a fact-finding mission led by its secretary general.

  • TajikistanMembers fought

    Kyrgyzstan and Tajikistan fought over their border in 2021 and 2022, killing more than 100 people. The two presidents signed a border treaty in March 2025.

  • UkraineRussia alone

    No other member sent troops to Russia's war. Belarus let Russian forces enter Ukraine from its territory. In 2022 Kazakhstan's president said it would not recognize the Donetsk and Luhansk "republics."

Why did Armenia freeze its CSTO membership?

Armenia froze its membership because the CSTO did not help it against Azerbaijan. After Azerbaijan attacked inside Armenia in September 2022, Prime Minister Nikol Pashinyan refused to sign the summit declaration that November. In September 2023 Azerbaijan took Nagorno-Karabakh and more than 100,000 Armenians fled. In February 2024 Pashinyan said Armenia had "frozen" its participation. It stopped paying dues in May 2024. In March 2025 its parliament passed a law to start the process of joining the EU.

Armenia has not formally left. Withdrawal requires six months' notice. Pashinyan's party won the June 2026 election with 49.75% and 64 of 105 seats. On August 24, 2026 he told parliament he would be "very pleased" if the CSTO expelled Armenia. Russia says Armenia remains a full member. Russia's 102nd base in Gyumri has a lease to 2044.

Armenia and the CSTO

  1. 1992Armenia signs the treaty in Tashkent
  2. 2022Azerbaijan attacks inside Armenia, the CSTO sends a fact-finding mission
  3. 2022Pashinyan refuses to sign the summit declaration in Yerevan
  4. 2023Azerbaijan retakes Nagorno-Karabakh, more than 100,000 Armenians flee
  5. 2024Armenia freezes its membership and stops paying dues
  6. 2025Armenia's parliament votes to begin the EU accession process
  7. 2026Pashinyan says he would be "very pleased" to be expelled

Is the CSTO Russia's NATO?

The CSTO is often called Russia's NATO, but it is much smaller and Russia dominates it. Russia has 74% of the members' people and 85% of their economy. In 2025 the six members spent about $196 billion on their armies. Russia's $190 billion was about 97% of the total. NATO's 32 members spent about eight times as much. Russia chairs the CSTO in 2026. In late September 2026 about 2,000 troops from five members held a CSTO exercise in Russia. Armenia stayed away.

CSTO and NATO, share of the world

  • CSTO
  • NATO

People, 2025

195 million · 2.4%
989 million · 12%

Economy, 2025

$3.05tn · 2.6%
$59.2tn · 50%

Military spending, 2025

$192bn · 6.6%
$1.57tn · 54%
People: UN. Economy: GDP at market exchange rates, IMF. Military spending: SIPRI, as a share of its world total of $2.9 trillion. The CSTO counts all six members, Armenia included. Military spending leaves out Kazakhstan, Kyrgyzstan, Tajikistan and Belarus, which have no figure. Military spending leaves out Iceland, Luxembourg, Bulgaria, Slovakia, Slovenia, Albania, Croatia, Montenegro and North Macedonia, which have no figure.

Is it in the CSTO?

Short answers for the countries people ask about most.

Is Armenia in the CSTO?

Frozen

Armenia is formally a member but froze its participation in February 2024, stopped paying dues and has sent no withdrawal notice.

Is Belarus in the CSTO?

Yes

A member since December 31, 1993. Russia says it has stationed nuclear weapons and its Oreshnik missile there.

Is Azerbaijan in the CSTO?

No

Azerbaijan joined in 1993 and left in 1999, objecting to Russia's military support for Armenia.

Is Georgia in the CSTO?

No

Georgia joined in 1993 and left in 1999. Its constitution still names NATO membership as a goal.

Is Uzbekistan in the CSTO?

No

A founder in 1992. Uzbekistan left in 1999, returned in 2006 and suspended its membership in 2012.

Is Ukraine in the CSTO?

No

Ukraine never signed the Collective Security Treaty.

Is Turkmenistan in the CSTO?

No

The UN recognized Turkmenistan's permanent neutrality in December 1995. It stays out of all military alliances.

Is China in the CSTO?

No

China and Russia are both in the Shanghai Cooperation Organisation, which has no mutual-defense clause.

Is Serbia in the CSTO?

No

Serbia's parliament has been an observer at the CSTO's Parliamentary Assembly since 2013. Serbia itself is not a member or observer.

Is Iran in the CSTO?

No

Iran is not a member, observer or partner of the CSTO.

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