The sudden, unexpected death this month of Iranian President Ebrahim Raisi, and the feverish speculation about the effect it will have on his country’s immediate future, is a reminder that the consequences of geopolitical events can rarely be predicted.

Iranians will go to the polls on June 28 to elect Raisi’s successor. But his death also prompted widespread guesswork about who might be Iran’s next supreme leader, the ultimate architect of the nation’s political direction.

Raisi was in the running to succeed 85-year-old Ayatollah Ali Khameini, who has been supreme leader since 1989. Following Raisi’s death, many now consider Khameini’s son, 55-year-old Mojtaba, the most likely successor.

But whoever becomes president, and whoever ultimately succeeds Khameini, Iran and its relations with the rest of the Middle East stand at a crossroads — and, as the origin story of the Islamic Republic demonstrates, the direction it takes next is as likely to be determined by external as well as internal forces.

Iran has been a Shiite theocracy, at odds not only with the West but also its Muslim neighbors, since the Islamic Revolution swept to power in 1979, catching the region and the wider world by surprise.

The immediate causes of the revolution, and the end of centuries of monarchical rule in Persia, were a growing sense of unhappiness among the Iranian people with the Shah’s perceived personal profiteering from the country’s oil wealth and the activities of the SAVAK, his hated secret police, and alarm among the conservative clerical class at his secular, pro-Western program of modernization.

But it was events set in motion by external forces two decades earlier that laid the groundwork for the Islamic Revolution in 1979 that created the Iran we know today and condemned the Middle East to decades of murderous meddling by Tehran.

In 1950, 12 years after oil was struck in Saudi Arabia, US-owned concession-holder the Arabian American Oil Company agreed, reasonably, to share its profits 50-50 with the Kingdom. Today, Aramco, which has been fully owned by the Saudi state since 1976, is one of the largest and most profitable companies in the world.

Across the Gulf in Persia, however, an inexplicably different story unfolded, with disastrous consequences.

At about the same time that the four US oil companies that originally owned Aramco agreed to share all profits evenly with Riyadh, in Persia the British government, the majority shareholder in the Anglo-Persian Oil Company, rejected outright a request from Tehran for similarly fair treatment.

That alone was bad enough, and represented a strangely ill-considered provocation at a time when the UK’s status as a world power was visibly shrinking, along with its once-dominant empire.

Britain’s humiliating invasion of Egypt in 1956, a last, desperate throw of the imperial dice, is seen as the moment the sun finally set on the British Empire. However, its all-but-forgotten meddling in Iran two years earlier would ultimately have even more far-reaching consequences.

In 1951, the democratically elected government of Iranian prime minister Mohammed Mosaddegh announced that, in the absence of a fair deal from the British, it would nationalize the country’s oil industry.

Britain’s reaction was the very definition of imperial highhandedness. The main concern of the UK government, struggling at the time to cope with the vast debts and costs of rebuilding it had inherited in the wake of the Second World War, was the loss of revenue from Iranian oil fields.

To get the US on side, it preyed on Washington’s Cold War paranoia and talked up the specter of the Soviet Union, Iran’s neighbor to the north, potentially infecting the country with its ideology of Communism.

The tactic worked. In 1953, Britain’s MI6 and America’s CIA engineered a plot to overthrow Mosaddegh and his government. As a result of Operation Ajax, hundreds were killed during fighting between the two sides, and the Western-backed Shah was installed to rule supreme.

It was a spectacularly rash decision that would disfigure the landscape of the Middle East for generations, and to this day serves as a case study for students of politics in the perils of the law of unintended consequences.

In time, the Shah dismissed parliament and in 1963 introduced a series of unpopular reforms that led to widespread poverty and overcrowding in cities and were condemned as anti-Islamic by Iran’s clerics.

A leading critic was Ayatollah Khomeini, one of the leaders of the Shiite community in the country. In 1963 he was jailed for a year before being exiled, settling first in Iraq and later in France. It was from Paris that he returned to Iran in triumph on Feb. 1, 1979, welcomed by delirious crowds as the leader of the revolution that had driven the Shah into exile. The rest, as they say, is history; a history that is still playing out as the world watches anxiously.