PARIS — Iran and the major world powers have reached an agreement on the Iranian nuclear program, putting an end to 21 months of negotiations that included this final round of more than 17 days of fierce talks in Vienna. Truth be told, the diplomatic standoff has been plaguing international relations for more than 12 years. Here is a brief timeline of the Iranian nuclear standoff:

2002 — Short-lived trust

After 23 years of delays, the first unit of the Bushehr Nuclear Power Plant, in southwestern Iran, begins operating. But with this first step forward toward legality, Iran takes two steps back. On Sept. 12 of the same year, two other nuclear facilities are discovered in Natanz and Arak, after revelations from regime opponent Alireza Jafarzadeh. The International Atomic Energy Agency (IAEA) reports the presence of enriched uranium in Natanz, and Iran is immediately suspected of working toward the production of nuclear weapons.

2003 — Outlined concessions

If for France, Germany and the UK, Iran is undoubtedly two-faced, let it be said that the agreement in force back then did not explicitly require Tehran to inform the IAEA of its projects. So this time, the European trio takes matters into its own hands and demands that Iran comply with the additional clauses of the Non-Proliferation Treaty (NPT), which includes unannounced visits from the agency.

Iran agrees in October 2003 and signs the treaty in December. The following year, Iran even announces that it would stop enriching uranium, though it is technically permitted within the rules established by the NPT.

2005 - A troublemaker arrives

Enter Mahmoud Ahmadinejad. Two months after his election in June 2005, the new president breaks the deal. The unpredictable leader declares shamelessly to the United Nations that Iran simply "has the right to develop a civil nuclear power program." And though he never mentions the possibility of building an atomic weapon at the time, the threat is veiled. Despite Western bans and U.S. calls for sanctions, Iran produces 3.5% enriched uranium, suitable for nuclear fission. In 2006, Ahmadinejad declares that "Iran has joined the group of countries with nuclear technology."

2006 — Quagmire and sanctions

Faced with Iran rushing in headlong, the IAEA sees no alternative but to hand over the dossier to the United Nations, which tries to find a way out with some form of compromise. The permanent members of the Security Council suggest providing financial assistance for the construction of light water reactors in exchange for an immediate halt to uranium enrichment. Iran refuses outright.

Faced with a dead end, the West has no choice but to punish Tehran. And so begins a worrying escalation — where with every sanction, Ahmadinejad retorts with a new provocation. In 2007, the Iranian president announces that the country boasts some 3,000 centrifuges and is therefore able to produce the dreaded nuclear bomb. Though increasingly isolated, and despite its banks being boycotted by the majority of world economies, Tehran carries on unabated.

2011 — Scary escalation

In late 2010, Iran is in possession of 20% enriched uranium, and reveals the presence of a secret new facility based in Fordu. For the U.S. and Israel, the atomic bomb is no longer a possibility — it's a reality. And though Ahmadinejad denies owning a operational warhead, a military intervention is now contemplated.

On Nov. 29, 2011, the black sheep of the United Nations announces the creation of 10 new uranium enrichment facilities. At the UN, the atmosphere is electric, with all members aware that a fateful spark to a potentially global conflict is at hand.

2013 — Cooling off

Ahmadinejad, though refusing to bow to what he calls the "Americano-Zionists," still has to abide by his country's laws. As his second term expires, he is succeeded by Hassan Rouhani, a more moderate, more diplomatic figure — and above all, a former Iranian nuclear negotiator from 2003 to 2005. From the outset, Rouhani calls for "serious and substantive" negotiations. "Iran is not a threat," he tells the United Nations.

On Sept. 27, 2013, Rouhani speaks by phone with U.S. President Barack Obama, the first act of its kind since the Islamic Revolution and American hostage-taking of 1979. Iranian Supreme Leader Ali Khamenei, meanwhile, takes a step forward too, announcing he is "not opposed" to a resumption of dialogue. The following month, negotiations begin in Geneva between the permanent members of the UN Security Council and a cordial, yet unwavering Iran. The major sticking point remains uranium enrichment, which Rouhani won't agree to stop.

2015 — Epilogue?

If some positions remain firm, Iran was ready to show its goodwill in exchange for a rapid repeal of the embargo. The obstacles that had blocked the road until the final hours were more form than substance. It is normal to doubt the reliability of a long-untrustworthy Iran. But one can also hope to receive a pledge of good faith from a country keen to revive its economy and willing to break with its eternal image of a pariah.