How Chemical Weapons Treaties Work — and Why States Still Evade Them

The Chemical Weapons Convention (CWC) is the world’s most comprehensive disarmament treaty, banning an entire category of weapons of mass destruction, yet recent discoveries of undeclared Syrian stockpiles reveal fundamental weaknesses in how the international community verifies compliance.

Syria’s accession to the CWC in 2013 followed the Ghouta chemical attack that killed more than 1,400 civilians. The Assad regime declared 1,300 tonnes of chemical agents and precursors, which were removed and destroyed under international supervision. But inspectors recently uncovered concealed caches of sarin and VX nerve agents at previously undeclared facilities, exposing a pattern of deception that persisted throughout the Verification process. The discovery illustrates a persistent challenge: the CWC framework depends on state cooperation, and regimes willing to lie face limited consequences.

The CWC Framework and OPCW Mandate

The CWC entered into force in 1997 and has 193 signatories, making it one of the most widely adopted Arms Control agreements. The treaty prohibits the development, production, stockpiling, and use of chemical weapons, requiring states to destroy existing arsenals within specified timelines. The Organisation for the Prohibition of Chemical Weapons (OPCW) administers the treaty from The Hague, conducting inspections and investigating alleged violations.

States parties must submit detailed declarations of chemical weapons stockpiles, production facilities, and relevant industrial sites within 30 days of joining. The OPCW then schedules systematic verification inspections at declared sites. Challenge inspections — where one state requests a short-notice inspection of another’s undeclared facility — are theoretically available but require executive council approval and have been invoked only once in the treaty’s 29-year history, by Russia against Ukraine in 2023.

The OPCW’s Technical Secretariat employs approximately 500 staff, including chemists, engineers, and inspectors. Annual budget constraints limit the organisation to roughly 300 inspections per year across all member states, a fraction of what comprehensive global monitoring would require. Most inspections focus on declared industrial facilities producing dual-use chemicals rather than suspected clandestine weapons programmes.

Syria’s Decade of Deception

Syria joined the CWC in September 2013 after the Ghouta attack drew international condemnation and threats of military intervention. The regime’s initial declaration listed 41 facilities and 1,300 tonnes of chemical agents. By mid-2014, the OPCW announced that all declared substances had been removed from Syrian territory and destroyed at sea aboard the U.S. vessel MV Cape Ray.

The narrative of successful disarmament collapsed in April 2017 when Syrian forces conducted a sarin attack on Khan Shaykhun, killing 89 people. An OPCW-UN Joint Investigative Mechanism report, according to OPCW, confirmed the regime’s responsibility, demonstrating that Syria had retained production capability and undeclared stocks. Subsequent attacks in Douma in 2018 involved chlorine, a dual-use industrial chemical not subject to the same declaration requirements as nerve agents.

The recent discovery of hidden sarin and VX caches followed a shift in territorial control during Syria’s ongoing civil conflict. Advancing opposition forces uncovered underground storage bunkers at military installations near Damascus that had never appeared in official declarations. The OPCW has since identified at least 20 additional “gaps, discrepancies and inconsistencies” in Syria’s initial submission, according to a May 2026 briefing by Director-General Fernando Arias.

Structural Limits of Verification

The CWC’s verification regime rests on three pillars: initial declarations, routine inspections, and challenge inspections. Each faces practical and political constraints that limit effectiveness against determined violators.

Initial declarations depend entirely on state honesty. Inspectors have no independent means of discovering undeclared sites without specific intelligence from member states or whistleblowers. The OPCW cannot compel satellite surveillance, signals intelligence, or defector testimony — it can only verify what states volunteer. Syria’s declaration was accepted at face value in 2013 despite widespread scepticism because the OPCW lacked evidence to challenge specific omissions.

Routine inspections focus on industrial facilities that produce dual-use chemicals, such as chlorine and phosphorus compounds used in agriculture and manufacturing. According to OPCW annual reporting, the organisation conducted 318 inspections in 2025 across all member states. Inspectors verify that declared quantities align with production records and that facilities lack prohibited weaponisation equipment. However, small-scale nerve agent production requires minimal infrastructure and can be concealed within legitimate pharmaceutical or pesticide plants. According to the Arms Control Association, a single 200-litre reactor vessel — easily hidden in a warehouse — can produce enough sarin to conduct multiple attacks.

Why Regimes Evade and Persist

Chemical weapons offer asymmetric advantages that conventional arms cannot match. They terrorise civilian populations, suppress internal dissent, and test international redlines without triggering the existential retaliation that nuclear use would invite. For regimes facing insurrection or seeking to project power regionally, the calculus often favours retention despite treaty obligations.

Syria maintained undeclared stockpiles because the benefits outweighed perceived risks. Chemical attacks allowed the regime to clear rebel-held urban areas without the artillery bombardments that would have required months and significant troop exposure. International condemnation proved manageable — Russia vetoed UN Security Council sanctions, and Western military responses remained limited to symbolic strikes on evacuated facilities.

The OPCW can refer non-compliant states to the UN Security Council, but enforcement requires political will that rarely materialises. Syria has faced 17 separate OPCW resolutions condemning its violations since 2017, yet remains a party in good standing with no material penalties beyond suspension of voting rights in 2021. Economic sanctions imposed by the U.S. and EU predate the chemical weapons discoveries and have proven ineffective at forcing compliance.

Implications for Non-Proliferation Credibility

The Syrian case exposes broader credibility challenges for the non-proliferation regime. If a state can join the CWC, fake disarmament, conduct multiple attacks, and face no meaningful enforcement, the treaty becomes a façade rather than a binding constraint. This dynamic has implications beyond chemical weapons.

The International Atomic Energy Agency (IAEA) operates with a budget nearly five times larger than the OPCW and has established precedents for intrusive inspections through its Additional Protocol framework. Yet even the IAEA faces compliance failures, as demonstrated by Iran’s recent obstruction of uranium monitoring following strikes that disabled cameras at enrichment sites. The loss of continuity of knowledge over 440 kilograms of near-weapons-grade material shows that verification regimes depend on continuous access, not just periodic verification.