The multilateral deal on Iran’s potential nuclear weapons program remains controversial. But the dividends of diplomacy were demonstrated during a series of extraordinary events in recent days.

Over the weekend, the International Atomic Energy Agency declared that among other milestones, Iran had reduced its low-enriched-uranium stockpile by 98 percent, dismantled 12,000 centrifuges, and removed and disabled the core of a nuclear reactor.

Those developments triggered “Implementation Day,” which led to the U.S., the U.N. and the European Union lifting nuclear-related sanctions. Iran got access to about $100 billion in frozen assets and settled a long-standing dispute with the U.S. over military equipment it paid for before the 1979 revolution. Iran now will be able to more easily sell oil on global markets, albeit at a time of plunging prices.

A subsequent U.S.-Iran prisoner exchange occurred, which freed five Americans, including Washington Post reporter Jason Rezaian. Days earlier, 10 U.S. sailors who had mistakenly navigated into Iran’s territorial waters were released in fewer than 24 hours, avoiding what could have developed into a destabilizing international crisis.

While these events are encouraging — and far preferable to a Mideast arms race or, even worse, yet another major Mideast war — there should be no illusion about the theocracy that has so horribly ruled Iran since the revolution. Iran remains a state sponsor of terror, has exacerbated sectarianism in Iraq, has prolonged the agony in Syria by backing Bashar Assad, and threatens Israel and Gulf states.

Of course Iran may be further emboldened by the billions in sanctions relief. And despite the recent halting progress, Iran’s bellicosity showed in recent ballistic missile tests, which led to additional non-nuclear sanctions applied by President Obama. Sanctions for human rights violations and support of terrorism will also remain in place, Obama said Sunday.

In a direct appeal to Iran’s citizens, Obama also noted the country’s great history and potential. But the recklessness of Iran’s rulers remains a threat. Should the deal hold, keeping a nuclear weapon out of their hands without resorting to war will be a major multilateral diplomatic accomplishment that should be emulated in defusing other rogue states.