A week after the United States and Iran signed a preliminary agreement aimed at ending the war, an Iranian drone crashed into a cargo ship sailing through the Strait of Hormuz.

There were no casualties or major damage, but the June 25 attack set off a chain of hostilities that would put the two countries on the path back to all-out war less than a month after they agreed to stop fighting.

Each attack and counterattack undermined the pillars of the agreement, which has now collapsed, although efforts are still underway to save it. The red lines marked by both parties have been crossed. A return to full-scale war that would further destabilize the Middle East and disrupt the global economy appears increasingly likely.

Here’s a look at how we got here.

The attack on the cargo ship came after Iran warned ships not to use an alternative route through the Strait of Hormuz that is overseen by the US military and intended to be outside Tehran’s control.

Iran had largely closed the waterway, which carried a fifth of the world’s traded oil and gas in peacetime, after the surprise attack by the United States and Israel on February 28 that started the war. Tehran has come to view control of the strait and its far-reaching economic impact as a key pressure point in its confrontation with the United States.

The preliminary agreement called for a full reopening of the strait, but also contained language suggesting Iran would manage traffic and potentially collect tariffs in the future. Iran has taken advantage of that, saying it has the right to control the strait and that the alternative route is a violation of the agreement.

The United States and others dispute this, saying the strait should be open to all and free, as it was before the war.

The United States launched strikes against Iran a day after the June 25 attack, hitting what the US military said were missile and drone locations and coastal radar sites.

The next day, Iran attacked an oil tanker using the alternative route through the strait, and the United States responded with more attacks. This time, Iran lashed out at nearby Gulf states, attacking Kuwait and Bahrain, countries hosting American troops.

The two sides withdrew the following week and each sent delegations to Qatar, which had played a key role in brokering the deal. But they did not meet directly.

Iran reiterated its warning against using the alternative route as it prepared for the day-long funeral of Supreme Leader Ayatollah Ali Khamenei, who was killed in the first US-Israeli strikes. The funeral began on July 4, with crowds calling for revenge against US President Donald Trump.

Days later, Iran attacked three ships in the Strait of Hormuz.

The United States responded with a wave of attacks that it said targeted air defense systems, radars and more than 60 small boats used by Iran’s paramilitary Revolutionary Guard. These boats have been used to harass ships in the strait.

The United States also revoked a waiver that had allowed Iran, for the first time in years, to sell its oil on the international market for US dollars. The resignation was part of the provisional agreement.

Iran condemned the US attacks and the reimposition of oil sanctions as violations of the deal, while insisting it had the right to control the strait, which the military command says is an “unbreakable red line.” Iran also expanded its retaliatory attacks, hitting Bahrain, Kuwait and mediator Qatar.

Trump, after leaving a NATO summit, offered mixed messages.

He said the US attacks were in response to attacks on shipping, and warned that “if it happens again, it will be much worse!” But he also appeared to rule out long-term military action, saying that “whatever happens will happen very quickly.” He also suggested that the US military could “just finish the job.”

The fighting has intensified steadily since then. On Wednesday, the United States reinstated its blockade of Iran’s ports, which had been lifted as part of the interim deal.

In recent days, the United States has expanded its attacks on northern Iran, hitting targets far from the strait. On Friday, it hit bridges and power plants in the south, collapsing a tower it said was used by the Revolutionary Guard for maritime surveillance at one of Iran’s main ports.

Iran said Friday that U.S. strikes have killed at least 46 people and wounded more than 400 since hostilities resumed.

Trump has repeatedly threatened to attack civilian infrastructure in Iran, and at one point earlier in the war he vowed to annihilate “the entire civilization” of Iran. So far, he has repeatedly walked back such threats, citing diplomatic developments.

But Iran’s leaders may already believe another line has been crossed. On Friday and Saturday, Iran attacked a water desalination plant in extremely arid Kuwait.

Trump has also mulled the possibility of taking control of the strait by force, possibly seizing one or more strategic islands held by Iran. That would likely require a much larger naval presence and potentially tens of thousands of ground troops.