For months, tension between the US and Iran has been simmering – with Washington urging allies not to do business in Tehran, and Iranian proxies or allies launching attacks at the US and its partners, including two ballistic missiles reportedly fired towards Jeddah and Mecca on Monday.

And the rhetoric is escalating. “In this face-off they are the ones who will be forced to retreat,” said Iran’s supreme leader, Ayatollah Ali Khamenei, in a speech last week. “If Iran wants to fight,” US president Donald Trump wrote in a tweet after a rocket fell about a mile from the US embassy compound in Baghdad on Sunday, “that will be the official end of Iran”.

Fears of a full-on war between the US and Iran have spiked in recent days. But the two countries and have been locked in a low-simmering conflict for decades.

It’s not a very cheery relationship. More often than not they have managed their considerable disagreements through threats, hostage-taking, economic blackmail, bombings and assassinations.

The conflict began shortly after Iran’s Islamic revolution, when students stormed the US embassy in Tehran in 1979, holding Americans hostage for 444 days, in an expression of anger for Washington’s quarter-century of support for the dictatorial monarch it installed after a 1953 CIA-backed coup.

Revolution in Iran: In pictures Show all 11 1 /11 Revolution in Iran: In pictures Revolution in Iran: In pictures A demonstration against the Shah in 1979 Getty Revolution in Iran: In pictures Armed women on guard in one of the main squares in Tehran at the beginning of the Iranian Revolution Getty Revolution in Iran: In pictures Demonstrators hold a poster of Ayatollah Ruhollah Khomeini, in January 1979, in Tehran, during a demonstration against the Shah AFP/Getty Revolution in Iran: In pictures Iranian rebels pose with a U.S. flag they bayonetted upside down on trees at Sultanabad Garrison northeast of Tehran on February 12 2019 AP Revolution in Iran: In pictures A gun battle in Khorramshahr during the revolution, 1979 Getty Revolution in Iran: In pictures Ayatollah Khomeini's supporters demonstrate in the streets of Tehran against the Shah among tear gas. The "black friday" caused the death of 200 people according to the Iranian government, 2000 according to the opposition, September 8 1978 AFP/Getty Revolution in Iran: In pictures Women wearing the traditional Chador demonstrate in the streets of Tehran against the Shah on September 7 1978 AFP/Getty Revolution in Iran: In pictures Demonstrators in Tehran calling for the replacement of the Shah of Iran during the Iranian Revolution, 1979. They carry placards depicting Ayatollah Mahmoud Talaghani, one of the leading revolutionaries Getty Revolution in Iran: In pictures Ayatollah Khomeini's supporters demonstrate in the streets of Tehran against the Shah. The "black friday" caused the death of 200 people according to the Iranian government, 2000 according to the opposition, September 8 1978 AFP/Getty Revolution in Iran: In pictures Thousands of the Ayatollah Khomeini's supporters on the streets of Tehran calling for the religious leader's return in January 1979 Getty Revolution in Iran: In pictures The Iranian Islamic Republic Army demonstrates in solidarity with people in the street during the Iranian revolution. They are carrying posters of the Ayatollah Khomeini, the Iranian religious and political leader Getty

The animosity continued during the 1980s, when Tehran’s allies bombed US embassies and military barracks, and the US torpedoed Iranian ships in the Persian Gulf. In the 1990s, the US sought to strangle and isolate Iran with sanctions, and Tehran did its part to blow up the Israeli-Palestinian peace deal that was supposed to herald the start of a new Middle East.

In the 2000s, the administration of George W Bush again ratcheted up the sanctions on Iran, threatening it with military action over its nuclear programme as it pursued its stillborn project to bring democracy to the Middle East, by way of Iraq.

Iran responded by handing out explosively formed penetrators to its proxies in Baghdad, where they devastated US armoured vehicles. Both sides launched cyberattacks against each other. Israelis, likely with US acquiescence, gunned down and blew up nuclear scientists in Tehran’s streets.

Accompanying the steady drumbeat of bombs was shrill rhetoric, each side’s threats and outrageous antics strengthening hardline counterparts. President Barack Obama and his team sought to end the cycle with the nuclear deal, which was meant to serve as a cornerstone for improving relations.

Mr Trump withdrew from the deal a year ago, promising to pressure Iran into submitting to “a better deal” that would encompass Tehran’s missile programme and its support for militant groups.

Ripping up the nuclear deal and resuming sanctions, the two countries’ relations have returned to default settings.

As the US has increased pressure, attempting to strangle Iran’s economy, Tehran has begun to respond. US decisions to remove waivers on all international oil trades with Iran coupled with the designation of the Revolutionary Guards as a terrorist organisation “created the consensus within the Iranian leadership that they need to escalate or impose some costs for the US behaviour”, according to Ellie Geranmayeh, an Iran expert at the European Council on Foreign Relations, adding: “The US has gone so far in cornering Iran that Iran is already in a state of war when it comes to the economic landscape.”

Iran already perceives itself as under attack, surrounded by US military hardware and personnel in the Arabian Peninsula, Iraq, Afghanistan and the Caucasus, and strangled by sanctions.

And the Trump administration has described Iran as the source of much of the world’s woes, calling it the world’s number one backer of terrorism and blaming it for everything from backing the Taliban to strengthening Nicolas Maduro in Venezuela.

Both Ayatollah Khamenei and Mr Trump have said they don’t want to push for an all-out war. But the US has begun positioning hardware and personnel in preparation for any attack.

Iranian officials, including major general Hussein Salami, the newly appointed chief of the Revolutionary Guards, have boasted in recent days that Iran too has set up networks, allies and infrastructure all over the region to exact costs on the US and its allies for Washington’s pressure campaign.

Sunday’s rocket attack towards the US embassy in Baghdad was seen as a message to the Americans, although there is no solid evidence it was necessarily directed at the outpost and it has as yet been unclaimed.

One European diplomat involved in Iranian affairs said they expected more “messages through proxies increasing in the coming weeks”.

Iran Supreme leader Ayatollah Ali Khamenei says Iran is 'not seeking war with US'

European officials have assured themselves that Mr Trump will restrain the more hardline players in his orbit, including his hawkish national security adviser John Bolton, who has long sought regime change in Iran and has publicly advocated for a campaign of airstrikes against the country.

Asked about Mr Trump’s latest tweet, threatening to destroy the entire Iranian nation, the European official quipped: “Which one? There are 10 a day.”

Others are less convinced of distance between the Trump and Bolton and other hardliners’ positions on Iran, or that it even matters what either thinks. Once the US scuttled the nuclear deal and chose the path of pressure, the longstanding dangerous state of affairs – the one Obama sought to dismantle – was inevitable .

“What is taking place now was all too predictable,” US Democratic Party lawmaker Adam Schiff, chairman of the House Intelligence Committee, told CBS News on Sunday, citing the administration’s decisions to pull out of the nuclear deal, label the Revolutionary Guard a terrorist organisation and up the rhetoric.