Tehran’s Milad Tower, the tallest structure in Iran, stands as a symbol of the revolutionary state’s engineering ambitions. Rising 435 metres, including its 120-metre antenna, the tower’s octagonal concrete shaft joins a pod with 12 floors housing observation decks, a cafe, and a museum. Above it, the antenna pierces Tehran’s smoggy skyline. From the deck of the 12th floor, the highest point accessible to visitors, one can take in the vast sprawl of the city, made the capital of the Persian Empire in the late 18th century by Agha Muhammad Khan, founder of the Qajar dynasty. To the north rise the Alborz mountains, the natural barrier separating the Iranian plateau from the Caspian Sea.

Inside the museum, a large 18th-century map of the Gulf drawn by a French cartographer is on display. “You may have heard some countries call the Persian Gulf the Arabian Gulf today,” a local travel assistant told this writer during a visit in February 2022. “Look at this map and reach your own conclusions.” A young woman, who described herself as “a huge fan” of Amitabh Bachchan and Aishwarya Rai, the assistant pointed to the mouth of the Gulf on the map. “This is the Strait of Hormuz,” she said. “This is the gate of the Persian Gulf. And the Iranians hold its key.” It is this geographical key that Iran used to effectively shut the strait after coming under attack by the U.S. and Israel on February 28.

The strait is a narrow corridor, 50 km wide at its entrance and exit, connecting the Persian Gulf waters to the Gulf of Oman, which joins the Arabian Sea. At its narrowest point, between Iran in the north and Oman’s Musandam Peninsula in the south — an exclave separated from mainland Oman by UAE territory — the waterway is just 33 km wide, which means it falls within the overlapping territorial waters of Iran and Oman (up to 12 nautical miles, or 22 km, from their coasts).

As the only gateway to the high seas from the Persian Gulf, the Hormuz Strait has remained one of the world’s most important waterways for centuries. In modern times, separate shipping lanes, as wide as 2 nautical miles, have been marked for inbound and outbound vessels. There is a buffer zone of around 2 nautical miles between the shipping lanes. So the tankers carrying fuel and gas typically navigated highly constrained waters even before the war.

In the 1980s, during the eight-year Iran-Iraq war, both sides targeted fuel tankers in the Persian Gulf, effectively weaponising the waters. In recent years, Iran has repeatedly warned that it would close the waterway if it came under attack. There are eight major islands in the strait, seven of which are controlled by Iran. Islands such as Qeshm, Hormuz, Larak, and Abu Musa sit closer to the shipping lanes, giving Iran a commanding physical advantage over the route. The ownership of Abu Musa, Greater Tunb, and Lesser Tunb islands is contested between Iran and the UAE, but they are de facto controlled and administered by Tehran. Since the 1970s, Iran has maintained a military presence on the islands.

Strategic significance

The strait’s strategic significance grew after the oil discoveries in the Persian Gulf region in the early 20th century. The post-War oil boom transformed the entire region. All Persian Gulf countries — Iran, Iraq, Saudi Arabia, Oman, Qatar, the UAE, Bahrain and Kuwait — have been more or less dependent on the strait to get access to the Arabian Sea. While Iran, Saudi Arabia, the UAE and Oman have ports outside the Gulf waters, others are fully dependent on Hormuz.

During 2023-25, 20% of the world’s liquefied natural gas (LNG) and 25% of seaborne oil passed through the strait. In 2025 alone, 20 million barrels of oil and oil products passed through this route every day, according to the U.S. Energy Information Administration. About 3,000 ships sailed through the strait each month before the war. Hormuz is also a key route for exports of fertilizer from the region, and Gulf countries import food, medicines and tech products through this route.

In June 2025, when Israel bombed Iran, Tehran’s response was largely limited to striking back at Israel. After the U.S. joined the war and attacked Iran’s nuclear facilities, Tehran carried out a token attack on the American base in Qatar and agreed to a ceasefire. The 12-Day War, as it’s known, did not pose any direct threat to traffic through the Strait of Hormuz. But in early 2026, when the U.S. was mobilising forces in the region amid threats of another war, Iran had warned that it would retaliate by striking American bases and shutting down the strait. The U.S. and Israel started the war on February 28 by assassinating Iran’s Supreme Leader Ayatollah Ali Khamenei, and Iran responded by doing what it had vowed to do. It retaliated by attacking Israel and Arab countries in the Gulf. And it took control of the strait. The number of ships passing through the strait daily, which was more than 100 before the war, fell by over 90%.

During the 40 days of bombing, the U.S. and Israel caused immense material damage to Iran. Its aerial and naval infrastructure has been repeatedly hit. But such attacks weren’t enough to force Iran, which used asymmetric warfare to weaponise the waters, to reopen the strait. Iran used cheap, disruptive weapons to impose disproportionate costs on the vessels that ignored its restrictions. Several ships that sought to pass the strait without the IRGC’s permission came under attack. Fuel prices started rising. Insurance and shipping costs soared. Energy-import-dependent economies, particularly India, were hit hard.

Contested terms

When U.S. President Donald Trump announced a ceasefire with Iran on April 8, he said Iran would reopen the Strait of Hormuz. The truce came into effect, but both sides differed on its terms. Iran demanded a ceasefire in Lebanon as well, but Israel actually stepped up the bombing of Lebanon. Mr. Trump later announced a ceasefire in Lebanon and “prevented” Israel from bombing the country — but the bombing campaign continued. When Iran refused to reopen the strait, Mr. Trump, on April 12, announced a blockade of Iranian ports. He said no Iranian ships would be allowed to pass through the American blockade in the Gulf of Oman. In response, Iran cancelled direct negotiations with the U.S., and pushed the nuclear file down its priority list.

Mr. Trump has repeatedly said that he was close to reaching a deal with Iran. He wants Iran to reopen the Strait in return for the lifting of the U.S. blockade. And Iran should abandon its nuclear programme. Iran, on its side, has established a new body, the Persian Gulf Strait Authority, to manage traffic through and maintain the Hormuz Strait, defying Mr. Trump’s demands. The PGSA has introduced a new email-based permit system for vessels and says all ships passing through the Strait should coordinate with the agency. Result: a diplomatic logjam.

One of Mr. Trump’s key demands for a deal today is that Iran should reopen the Strait of Hormuz, which was fully open before Mr. Trump and his ally Benjamin Netanyahu launched this war on February 28.