BERLIN—The framework nuclear agreement reached with Iran after intense negotiations in Lausanne does not mean a deal is done. The final text, to be agreed by June 30, still has to ensure that in return for lifting sanctions, Iran will not be able to build a nuclear bomb in less than a year. But that did not stop thousands from celebrating the crucial breakthrough in the streets of Tehran. Meanwhile, U.S. President Barack Obama said that the core objectives had been reached, German Foreign Minister Frank-Walter Steinmeier declared his satisfaction, and the other members of the P5+1 (the five permanent members of the UN Security Council plus Germany) were equally positive.

But not everyone is happy. Israeli Prime Minister Benjamin Netanyahu has said that Israel will not accept the deal, and neither will many Republicans in Washington. The questions at the crux of the negotiations have been the same since 2003: Is trust possible? If so, how much? President Obama put it succinctly: “This agreement is not based on trust, but on verification.”

One need not look back very far to find sufficient reason to be distrustful of Iranian intentions. Demands for Israel’s annihilation, arms deliveries to rebel groups in Lebanon and Yemen, support to Hamas and Bashar al-Assad’s Syria, attempts to have purported critics murdered, and the development of long-range missiles all contribute to skepticism. And, from Iran’s point of view, there were compelling reasons to go nuclear. The West stood by when Iraq used chemical weapons against Iran. A U.S. president categorized Iran as part of the “axis of evil.” And the international community has remained silent about Israel’s rumored possession of the bomb.

Considering those factors, why did Iran agree to negotiate in the first place? Why did it not leave the International Atomic Energy Agency (IAEA) and the Nuclear Non-proliferation Treaty (NPT)? Although Iran had not formally violated the NPT at the time, Germany, France, Britain, and the EU commenced talks in 2003, leading to Iran permitting inspections and voluntarily suspending enrichment. This process was broken off in 2005 by the new Iranian President Mahmoud Ahmadinejad. In 2006, the “EU-3” were joined by the United States, Russia, and China to form the P5+1.

Soon a pattern evolved. Talks repeatedly foundered, followed by sanction resolutions adopted by the UN Security Council and implemented by the United States, EU countries, Japan, and a number of others. (Although not by everyone; China, despite being party to the P5+1 talks, increased its market share in Iran from 8 percent in 2006 to 36 percent today.) Iran’s enrichment and construction of centrifuges continued and the sanctions gradually toughened. The P5+1 became more distrustful of Iran’s good intentions, and Iran became increasingly averse to submitting to any kind of international control. However, the sanctions took their toll on the Iranian economy, and on everyday life.

The Iranian objective finally boiled down to avoiding any inspection and verification measures regarded as discriminating, and the lifting of sanctions as soon as possible. The P5+1 focused on obtaining a long-term inspection regime that would satisfy the IAEA’s demands. Over the years, two obstacles that stood in the way of success reappeared regularly. One was uncertainty on the part of the P5+1 as to how far Iran’s civilian nuclear program could be tolerated without constituting a risk to regional security. The second was the intransigence of hardliners in Tehran who refused any kind of discriminatory inspection regime that could be seen as violating Iran’s sovereign right to pursue a civilian nuclear program. Only after Hassan Rouhani became Iran’s president in 2013 did Iran’s leadership approach the lifting of sanctions as a major step for Iran to advance its economy, its industry, and its place in the world. Netanyahu also effectively diminished Israel’s influence by declaring that Israel could never accept any deal that allowed Iran to keep even a civilian nuclear program.

The exuberant excitement in Tehran’s streets after the Lausanne deal was struck indicates at least one thing: the sanctions worked. Now, to find a way to realize the hopes of the Iranian people and make sure that Iran will indeed never become a nuclear threat, the framework agreement will need reliable tools. This requires an agreement on inspections and verification measures in exchange for lifting financial sanctions, the export of Iran’s enriched uranium in exchange for fuel rods, the dismantling of the majority of centrifuges to reach a minimal breakout period of one year in exchange for a gradual lifting of economic sanctions, and the approval of the UN Security Council. All of this seems possible.

Then, the world would be spared the threat of an even less peaceful Middle East. Israel would also be safer for it, the misgivings of Israeli hawks notwithstanding. The 35-year cold war between the United States and Iran may possibly be at an end. Trust may not have been present at the start of the process, but it is necessary if the agreement is to work in the long term. In order to build such trust, controls will be necessary for some time. This is what will have to be worked out between now and June 30.

Volker Stanzel is an incoming senior advisor to The German Marshall Fund of the United States.

Read the accompanying piece: The Significance of the Iran Nuclear Talks Exceeds Any Final Agreement