Tehran, 1953

The Anglo-Iranian Oil Company was British, it operated in Iran, and the terms were what a reader might expect for an agreement signed in 1933 between an empire and a country it could pressure.

In 1951 Iran's parliament voted to nationalise it, and Mohammad Mossadegh became prime minister. Britain responded with a boycott and a blockade of Iranian oil exports, took the case to the International Court of Justice and lost, and began pressing Washington to remove the government. Truman declined. Eisenhower, taking office in 1953 with the Cold War as the organising frame of American policy, did not.

The operation was TPAJAX to the CIA and Boot to MI6. Its methods are set out in the agency's own history: propaganda planted in the Iranian press, payments to members of parliament, cultivation of the Shah, organised street demonstrations, and contact with sympathetic officers. A first attempt on 16 August 1953 failed and the Shah fled the country. A second attempt on 19 August succeeded. Mossadegh was arrested and tried; the Shah returned and ruled until 1979.

The CIA acknowledged all of this in 2013, in a document titled The Battle for Iran, which states that the coup was carried out under CIA direction as an act of United States foreign policy.

So far, so settled. Now the part that is not.

Historians disagree seriously about how much the outcome depended on the operation. Ervand Abrahamian treats the covert action as decisive and the domestic opposition as insufficient without it. Ray Takeyh argues that Iranian actors, the clergy, the bazaar, the army and a fracturing coalition around Mossadegh, were the primary cause, and that the agency overstated its own contribution in documents written to justify its budget.

That second point deserves attention, because it cuts against an instinct most readers have. An internal operational history is excellent evidence of intent and considerably weaker evidence of causation. An organisation describing its own success is not a neutral witness to it. People drop this distinction in both directions: sceptics use it to wave away the documents entirely, and critics use the documents as though the agency's self-assessment were a finding of fact.

The defensible summary is narrow and worth stating precisely. The United States and the United Kingdom set out to overthrow an elected government, spent money and effort attempting it, and the government fell. How much of the falling they caused is not fully knowable, and honest people who have read the same files disagree.

What is not in dispute is the accounting.

The operation is often described as the cheapest foreign policy success in American history, and by the measure used in 1953 it was. The Shah signed the agreements. The oil flowed. The immediate objective was met at trivial cost. The measure used in 1953 covered one year, and the consequences of that year were still being paid twenty-six years later, when a revolution explicitly hostile to the United States replaced the government it had helped restore.

Whether 1953 caused 1979 is the argument. That 1953 was never priced against 1979 is not.