What was in the agreement
The Joint Comprehensive Plan of Action (signed July 2015, implemented January 2016) limited Iran's enrichment to 3.67% for fifteen years, capped its stockpile at 300 kg of low-enriched uranium, restricted advanced centrifuge use, and submitted Iran to an enhanced safeguards regime under the IAEA Additional Protocol. In exchange, the P5+1 (US, UK, France, Russia, China, Germany) committed to lifting nuclear-related sanctions.
What broke it
The US withdrew unilaterally in May 2018 under the Trump administration, reimposing and expanding sanctions. Iran responded over the following year by progressively breaching the agreement's enrichment and stockpile limits. Subsequent attempts to revive the agreement under the Biden administration did not produce a renewed deal.
Why it still matters
The technical architecture of the JCPOA — enrichment caps, stockpile limits, advanced-centrifuge restrictions, IAEA Additional Protocol monitoring — is the template most current diplomatic proposals modify rather than replace. Any future agreement will be measured against the JCPOA baseline.
The sunset clauses
Several of the agreement's key restrictions had pre-defined expiry dates (the "sunset" clauses). The fact that the JCPOA was a temporary architecture rather than a permanent ban is part of why successor proposals have struggled to win consensus on either side.