On November 5, 2018, the Trump administration restored all the penalties it had lifted from Iran as part of a nuclear agreement made in 2015. This was the final step in a decision to abandon that agreement, and it wiped out the financial relief that had made the deal work in the first place.

The penalties focused on Iran's oil industry and shipping — two of its most important sources of income. According to a State Department briefing from November 2, 2018, the administration said it was applying "maximum pressure" to force Iran to accept new terms not only on nuclear weapons but also on its missile program and military activities in the Middle East.

To understand what was lost, it helps to know how the original 2015 deal worked. That agreement, signed by Iran, the United States, Russia, China, France, the United Kingdom, Germany, and the European Union, was a trade: Iran would limit how much nuclear fuel it produced and accept inspections to prove it. In return, the world's major powers would remove the penalties — sanctions — that had strangled Iran's economy. Economic relief was the reward that made Iran willing to accept limits on its nuclear program.

The administration reimposed the penalties in stages. It withdrew from the deal in May 2018, but the sanctions came back in waves. A first set in August targeted various industries. On November 5, the bigger blow fell: the penalties on oil sales, shipping, and Iran's central bank. Together, they brought back nearly all the penalties that had been in place before the 2015 deal, with some new additions.

The results came fast. Iran's oil sales, which had bounced back after 2015, dropped sharply. Buyers in Europe and Asia worried about U.S. punishment — if they kept buying Iranian oil, America could penalize them too. This threat is called a "secondary sanction." Major European companies began shutting down their operations in Iran even before November, knowing the deadline was coming. Three European countries — France, Germany, and the United Kingdom — tried to create a separate way to do business with Iran without using U.S. dollars, but it did not work well in practice.

The other countries that had signed the 2015 deal did not leave it when America did. Russia, China, France, Germany, the United Kingdom, and the EU said they wanted to stay. Iran also stayed in the agreement on paper, but starting in 2019, it began breaking its promises. It produced more enriched uranium than allowed. Later, it made uranium enriched to 60 percent — much higher than the deal permitted. By the mid-2020s, Iran's nuclear program had grown far beyond what the agreement said it could.

The lessons from 2018 are still shaping negotiations today. Talks about returning to the deal, or making a new one, have hit roadblocks over who should move first — does America lift sanctions, or does Iran limit its nuclear program? — and over what would be included. The nuclear work Iran did while under maximum pressure made things harder: the gap between where Iran is now and where the deal said it should be has grown wider, and checking on Iran's promises has become more complicated.

Sanctions are a tool that works in two ways. The U.S. can turn them on and off easily, but once they damage a country's economy, that damage does not heal quickly. Companies that left Iran after 2018 did not come back fast even when there were chances to do business again. It takes a long time to rebuild trade networks and banking connections once they are broken. This is why any future deal would need to account for how long it actually takes for Iran's economy to recover — something that could determine whether any agreement holds.