The war did not emerge from nowhere. It was the product of a sequence of escalating confrontations that began in 2023 and accelerated through 2025 — each step raising the probability of the next, each diplomatic failure narrowing the available exits. Understanding the buildup is not merely historical. It establishes the character of the conflict — specifically, that it arrived over a period long enough for markets to price in geopolitical risk in theory while failing to price in the actual mechanics of a Hormuz closure in practice.

The key inflection point was June 2025, when the United States and Israel conducted what they termed Operation Midnight Hammer — a 12-day campaign targeting Iranian nuclear facilities. Iran, despite preparations to mine the Strait of Hormuz and a parliamentary vote supporting closure, ultimately refrained from closing it. Markets spiked briefly and recovered. The lesson institutional memory drew from that experience was that Iran would threaten but not follow through. That inference proved incorrect when the conditions changed.

What changed in February 2026 was the target set. The June 2025 strikes had degraded Iranian nuclear capabilities while leaving the regime's leadership intact and with something to preserve. The February 28 operation, codenamed Operation Epic Fury by the US and Operation Roaring Lion by Israel, was categorically different: it killed Supreme Leader Ali Khamenei — the person who had been the system's rational constraint — along with 48 or more senior officials including the IRGC commander, the Defense Minister, and the chief of staff of the Iranian Armed Forces. A regime that had maintained its deterrent calculus because it had leadership with survivability incentives was replaced, overnight, by a succession struggle operating under existential pressure. The calculus against Hormuz closure — weigh the economic consequences to global markets against the military response — no longer applied to a command structure fighting for its survival.

In the days before the strikes, intelligence available to Oman had suggested a nuclear deal was near: Iran had agreed in principle to eliminate its enriched uranium stockpile and accept IAEA verification. Those talks were overtaken by events. On the eve of the attack, Iran held 55 kg of weapons-grade 90%-enriched uranium — enough, by IAEA calculations, for two to three nuclear devices. Whether the decision to strike rather than conclude the diplomatic process reflected a judgment that Iran could not be trusted to comply, or a prioritization of regime change over nuclear constraint, has not been resolved in public reporting. What is not disputed is the sequence: diplomacy was within reach, the strikes proceeded, and the Hormuz closure followed.

The Strait of Hormuz is 21 nautical miles wide at its narrowest point. It sits between Iran to the north and Oman to the south. It is the only maritime exit from the Persian Gulf to the open ocean, and through it flows, in normal conditions, approximately 20 million barrels of crude oil per day — one-fifth of all globally traded oil. The five Gulf producers whose oil must transit the strait — Saudi Arabia, Iraq, Kuwait, the UAE, and Iran itself — have no alternative route that approaches this volume.

The alternative pipeline infrastructure that exists cannot substitute for a sustained Hormuz closure. The East-West Pipeline across Saudi Arabia can carry roughly 5 million barrels per day — about 4 million of which represent Saudi production that can be rerouted. The Habshan-Fujairah pipeline in the UAE can carry an additional 1.5 million barrels per day of Abu Dhabi crude to the Gulf of Oman. In total, available pipeline bypass capacity represents approximately 17% of normal Hormuz flows — and even that capacity faces operational constraints given that Gulf storage is now depleted from Iran's pre-war attempts to reduce vulnerability. Crucially, pipeline bypass applies only to crude oil. Liquefied natural gas cannot be routed via pipeline. Sulfur cannot. The roughly 1,000 other commodity flows that transit the strait cannot.

The strategic reserve release announced by the IEA on March 11 — 400 million barrels, the largest in history — addresses the oil component of the disruption. It does not address the LNG, fertilizer, sulfur, helium, or industrial commodity dimensions. Even on oil, it is explicitly described by the IEA as a "stop-gap measure" contingent on a swift resolution to the conflict. At current disruption levels, the released reserves represent approximately 20 days of the volumes normally transiting the strait.

What makes the current closure structurally different from the prior geopolitical episodes that produced temporary oil price spikes is that this disruption has already changed shipping behavior and insurance availability, not merely market expectations. In every prior near-miss — the 2020 Soleimani strike, the 2024 Iran-Israel exchanges, the June 2025 twelve-day war — ships continued to transit, insurance remained available, and the disruption was priced as a future risk. The current closure is a present reality: Maersk and Hapag-Lloyd have suspended Mideast routes, P&I clubs have withdrawn war risk coverage for Hormuz transit, and approximately 170 container ships with 450,000 TEU of combined capacity were trapped inside the strait as of March 1. The key variable is no longer whether a spike occurs — it has occurred — but how long the disruption persists.

An oil price shock of this magnitude — roughly 40% in thirteen days, with the futures curve indicating sustained elevated pricing — transmits into the US economy through four primary channels. Each channel is consequential independently. Their interaction, in the specific economic environment that preceded the shock, is the part that standard scenario analysis consistently underweights.

The first channel is direct consumer cost inflation. Oil prices flow through to gasoline prices with a short lag — typically one to two weeks — and then to diesel, jet fuel, heating oil, and petrochemical feedstocks with somewhat longer lags. Goldman Sachs estimates that sustained 10% oil price increases add approximately 0.2 percentage points to overall inflation. A 40% shock, if sustained, adds roughly 0.8 percentage points — against a pre-conflict baseline in which tariff-driven inflation had already added over 70 basis points to core CPI. The two inflation vectors are not additive in a simple mathematical sense: they interact through wage expectations, business pricing behavior, and consumer confidence in ways that make the combined impact larger than the sum of parts.

The second channel is the Fed's policy constraint deepening. Before the conflict began, the Fed was already navigating a stagflation trap: inflation above target, growth signals weakening, policy tools compromised by fiscal dominance. The geopolitical shock narrows the available path further. Goldman pushed its expected rate cuts back to September and December. Former Fed Chair Yellen stated explicitly that the war makes the Fed's inflation-control job more difficult. A supply-side energy shock that the Fed cannot address through rate policy — rate hikes cannot produce more oil — forces the central bank into an even tighter paralysis: raise rates and risk accelerating the growth slowdown, hold rates and allow inflation to de-anchor.

The third channel is business investment and employment suppression. The uncertainty injected by a geopolitical shock of this character — ongoing war, unclear duration, unclear diplomatic resolution path, new supreme leader with unclear policy posture — suppresses capital expenditure and hiring decisions in precisely the sectors most sensitive to energy costs and supply chain stability. Goldman's February payroll data — a 92,000 decline — was already a warning signal before the conflict began. The war adds a layer of uncertainty that makes corporate investment decisions rationally deferrable.

The fourth channel is the one most specific to the environment documented in Parts I through III: the interaction effect between geopolitical shock and existing structural vulnerabilities. Corporate debt refinancing walls, commercial real estate stress, and private credit fragility (documented in Part II) do not operate independently of an energy price shock. A business facing a 2026 debt maturity wall in an environment of elevated rates makes a different refinancing calculation in an environment of slowing growth and rising energy costs than it does in an environment of stable growth. The geopolitical shock does not create these vulnerabilities — it applies pressure to vulnerabilities that already exist, at a moment when they are most exposed.

Every credible scenario analysis of the Iran war's economic impact converges on the same organizing variable: duration of the Hormuz disruption. The magnitude of the military operation, the status of the Iranian regime, the posture of proxy forces — all of these affect the probability distribution over duration scenarios. But the economic consequence function is dominated by one input: how many weeks or months does the strait remain effectively closed to commercial shipping?

The scenario analysis below incorporates Goldman Sachs, Oxford Economics, the IEA, and the Energy Policy Institute at the University of Chicago. Three scenarios span the realistic range from as-of-publication market conditions through the tail risk that all credible analysts acknowledge but that financial markets appear to be pricing with insufficient weight.

The United States has absorbed major oil price shocks before: the 1973 OPEC embargo, the 1979 Iranian Revolution, the 1990 Gulf War, the 2004–2008 commodity supercycle, the 2022 Russia-Ukraine energy shock. Each produced significant economic disruption. None produced a US recession directly and immediately attributable to the oil shock alone. This history provides the basis for institutional reassurance — "we've weathered this before" — that deserves examination rather than acceptance.

The critical difference between prior shocks and the current one is not the magnitude of the price spike, though this closure is already characterized by the IEA as the largest disruption to global oil supply in history. The critical differences are structural and compound.