Conditional branches on the Hormuz regime, the Yemen front, Israel–Hezbollah and the US commitment
ABSTRACT
This simulation maps the forms the Gulf security architecture can take in 2027 from four variables fixed at September 2026 values: the Hormuz regime, the Yemen–Red Sea front, the Israel–Hezbollah front and the US commitment. It derives three conditional branches without probabilities: negotiated opening, chronic restriction and two-chokepoint escalation. The architecture is moving from a US-centred structure to a layered, fragmented one. Only the United States can change the Hormuz regime, while Red Sea and Yemen security shifts to Saudi-led coalitions and to the Mecca Joint Defence Agreement, which has produced no troop commitments. The US–Iran bargain decides the 2027 outcome first and the Yemen front’s decoupling second; regional alliances adapt to the outcome rather than shape it.
1. Purpose and method
Seven months after US and Israeli strikes on Iran began the war on 28 February 2026, the Gulf security order is strained at two chokepoints. Hormuz transit has been restricted since early March, and the Houthi–Saudi front, reopened in July, threatens the Yanbu route Saudi Arabia uses to bypass Hormuz. Security architecture here means the actors protecting regional sea lanes and energy infrastructure, their mutual commitments and the degree to which those commitments are exercised. Scope is October 2026 to 2027; the actors are the United States, Iran, Saudi Arabia, the Houthis, Türkiye and Pakistan.
Each branch states a condition, mechanism, arithmetic and indicators; branches are conditional and probabilities are not assigned. Gholz and Press (2010) argue that oil markets absorb most supply disruptions through price and trade rerouting, so that US military presence is necessary only in a limited set of scenarios. Tang (2009) defines the security dilemma as defensive steps, taken under uncertainty about intentions, being read as threats so that mutual insecurity rises.
2. The published baseline
Hormuz: Argus’s transit and flow figures appear in the table below; CENTCOM’s 44 “assisted transits” on 1–2 September (Argus Media, 2026) show the United States escorting commercial ships while blockading Iranian ports.
US–Iran bargaining: Iran’s seven-day plan makes a halt to regional conflicts, including Lebanon and Yemen, a precondition for reopening Hormuz (AFP, 2026). Trump rejected the proposal, according to a Wall Street Journal report (Holland & Hafezi, 2026), and expects a deal “right after the election” (Schuler, 2026).
Yemen–Red Sea: in the two weeks to 10 September at least 194 people were killed and 880 wounded in Taiz, the west coast, al-Jawf, Marib and Dhale, and the Houthis captured Mocha (Al Jazeera, 2026a). Bab el-Mandeb transit figures are 27 July–23 August weekly averages (Lloyd’s List Intelligence, 2026). On 15 September the Houthis’ acting foreign minister, Abu Ras, said the group had no intention of shutting down Red Sea shipping (Lucente, 2026).
Israel–Hezbollah: Israeli strikes on 6 September killed 4 and wounded 6, and President Aoun’s office called them a “dangerous escalation” (Tolba, 2026).
US commitment: the Strategic Defence Agreement signed with Saudi Arabia in November 2025 is an executive agreement, not a Senate-ratified treaty (Martinez, 2025). Rubio said on 23 September that Washington would honour its commitments (Arab News Pakistan, 2026); according to Semafor, the administration had provided no military aid and Pakistan and Türkiye had not committed troops (Gonzalez, 2026). Al Jazeera, which dates the signing of the Mecca agreement to 7 August, reports that its attack-on-one-is-attack-on-all clause had not been formally invoked as of 25 September; France confirmed sending troops, radar and defence systems to the Yanbu terminal (Al Jazeera, 2026b). Saudi Arabia faces an interceptor shortage linked to depleted US stocks and has sought air-defence help from France, Britain, Pakistan and Egypt (Magdy et al., 2026). The East–West pipeline restarted at low flow on 22 September, with full capacity expected in 6–8 weeks (Yap et al., 2026).
3. The identifying assumption set
| Parameter | Value | Source |
|---|---|---|
| H1 Hormuz transits, 2 September / pre-war | 9 / ~135 ships a day | Argus Media (2026) |
| H2 Assisted transits | 44 on 1–2 September | Argus Media (2026) |
| H3 Gulf crude flow / via Hormuz (28-day) | 7.54 / 5.04 mb/d | Argus Media (2026) |
| R1 Bab el-Mandeb weekly transits | 319 → 273 | Lloyd’s List Intelligence (2026) |
| R2 Taiz front to Bab el-Mandeb | ~60 km | Al Jazeera (2026a) |
| L1 Lebanon deaths, 2 March–6 September | >4,300 | Tolba (2026) |
| P1 Pipeline full capacity | 6–8 weeks from 22 September | Yap et al. (2026) |
The identifying assumption is a hierarchy. Because the seven-day plan ties Hormuz to Lebanon and Yemen, the US–Iran bargain is the primary variable, the two fronts are secondary variables that may couple to or decouple from it, and alliances such as the Mecca agreement and the Saudi-led Red Sea coalition are dependent variables.
4. Branch A: Negotiated opening
Condition: after November 2026, US–Iran talks produce a sequenced deal that pairs lifting the blockade with reopening Hormuz.
Mechanism: the US role shifts from blockader to protector and the Mecca agreement loses urgency. Yemeni ground fighting can continue, because Houthi territorial gains reflect local aims that a US–Iran deal does not reverse.
Arithmetic: H1 puts transits at 6.7% of the pre-war level (9 / 135). Assisted transits averaged 22 a day (44 / 2), or 16% of pre-war traffic (22 / 135); restoring pre-war volume through them alone would take about six times September’s throughput (135 / 22 = 6.1). Normalisation therefore requires ordinary transits to replace assisted ones, which only a political settlement provides.
Indicators: a timetable matching blockade relief to reopening; ordinary transits replacing assisted ones; fewer Houthi attacks on Saudi territory.
5. Branch B: Chronic restriction
Condition: no agreement, and both sides keep absorbing current costs.
Mechanism: layered fragmentation. The United States holds Hormuz, the Saudi-led coalition and France hold the Red Sea, and the Mecca agreement stays at the consultative level. September data place the starting conditions closest to this branch.
Arithmetic: from H3, 2.50 mb/d of Gulf crude (7.54 − 5.04), or 33%, moved by routes that avoid the strait, and the East–West pipeline, one of those routes, regains full capacity only in the 3–17 November window (P1). R1 is a 14.4% fall, against a 93.3% fall in Hormuz transits (1 − 9 / 135), so the Red Sea constraint is still secondary. Yemeni fighting ran at about 14 deaths a day in early September (194 / 14).
Indicators: single-digit daily Hormuz transits and continuing tanker strikes; Yemeni front lines settling into attrition.
6. Branch C: Two-chokepoint escalation
Condition: the Houthis close Bab el-Mandeb to commercial shipping, or the Lebanon front returns to full-scale war.
Mechanism: the US commitment and the Mecca agreement’s mutual-defence clause are tested at the same time. This is the limited class of scenario in which Gholz and Press (2010) see US military presence as necessary. Interceptor scarcity makes Saudi defence depend on several partners, each contributing little. Following Tang (2009), alliance texts without troop commitments give Riyadh limited protection while feeding Iranian and Houthi perceptions of encirclement, which lowers their deterrent yield and raises escalation risk.
Arithmetic: 85.6% of the Bab el-Mandeb baseline is still moving (273 / 319); closure would remove it on top of Hormuz’s 93.3% transit loss. Lebanon’s toll averages more than 22.9 deaths a day over 188 days (4,300 / 188), well above the 4 deaths of 6 September; daily tolls approaching that average would signal a return to full-scale war.
Indicators: reversal of Abu Ras’s statement; the Taiz front reaching the Bab el-Mandeb coast; a sudden fall in Bab el-Mandeb and Suez transits. Unverified Houthi claims, such as an F-15 downing (Magdy et al., 2026), are not indicators.
7. Failure conditions and limitations
The hierarchy fails if Israel, which is not a party to the US–Iran bargain, keeps the Lebanon front active after a deal, because Lebanon is one of Iran’s own preconditions; Branch A would then stall even with US–Iran agreement. It also fails if Washington revises the Saudi commitment, which as an executive agreement needs no Senate action to change. Yemeni casualty figures differ by source and period, so only Al Jazeera’s two-week figure is used; the Lebanon average rests on a cumulative “more than” figure and one day’s toll; transit counts follow Argus’s metric; and the Mecca agreement’s text is not officially verified.
8. Outlook: Türkiye, Saudi Arabia and the World
October 2026 brings expectations rather than outcomes. The pipeline’s 3–17 November window keeps Saudi non-Hormuz export capacity constrained until then (Yap et al., 2026). Trump’s post-election expectation (Schuler, 2026) places the earliest Branch A after November. The emergency meeting of chiefs of staff agreed by the three foreign ministers on 24 September (Al Jazeera, 2026b) will be the first sign of whether the alliance moves from coordination to command.
For Türkiye the deciding question is whether the Mecca clause is invoked. In Branch B Ankara can stay at coordination and intelligence sharing and avoid direct combat with the Houthis; in Branch C its refusal to commit troops would weaken the agreement’s credibility. As Iran’s neighbour, Türkiye would bear the cost of Tang’s dilemma directly if Tehran read invocation as a threat.
For Saudi Arabia, Branch B is the most costly path: Yanbu remains a target, and Riyadh keeps adding partners to reduce reliance on a single patron.
Globally, the two chokepoints rest on weakly coordinated coalitions rather than one commitment; Branch C marks that order’s limit.
9. Conclusion
At the end of September 2026 the Gulf security architecture is layered and fragmented. Only the United States, which blockades and escorts at once, can change the Hormuz regime, and reopening depends on the US–Iran bargain. Red Sea and Yemen security is spread across a Saudi-led coalition, France’s Yanbu deployment and a Mecca agreement without troop commitments. Iran’s Hormuz conditions make any deal depend on Israel and the Houthis, who are outside the bargain. Chronic restriction is closest to the starting conditions; negotiated opening depends on the post-November US–Iran calendar and two-chokepoint escalation on Houthi conduct at Bab el-Mandeb. Regional alliances will adapt to those outcomes in 2027 rather than determine them.
SOURCES
AFP. (2026, 26 September). Iran offers seven-day plan to reopen Strait of Hormuz. The Vibes. https://www.thevibes.com/articles/world/127695/iran-offers-seven-day-plan-to-reopen-strait-of-hormuz
Al Jazeera. (2026a, 10 September). Houthis, Yemeni forces engaged in fierce battles: Why each front matters. https://www.aljazeera.com/news/2026/9/10/houthis-yemeni-forces-engaged-in-fierce-battles-why-each-front-matters
Al Jazeera. (2026b, 25 September). Saudi Arabia allies line up support as Houthi attacks mount. https://www.aljazeera.com/news/2026/9/25/saudi-arabia-allies-line-up-support-as-houthi-attacks-mount
Arab News Pakistan. (2026, 23 September). US will honour defense commitments to Saudi Arabia, Rubio says. https://www.arabnews.pk/saudi-arabia/us-will-honour-defense-commitments-to-saudi-arabia-rubio-says-3002132
Argus Media. (2026, 3 September). Hormuz traffic at 9 vessels: Update. https://www.argusmedia.com/en/news-and-insights/latest-market-news/2873472-hormuz-traffic-at-9-vessels-update
Gholz, E., & Press, D. G. (2010). Protecting “the prize”: Oil and the U.S. national interest. Security Studies, 19(3), 453–485. https://doi.org/10.1080/09636412.2010.505865
Gonzalez, J. (2026, 25 September). Saudi Arabia intercepts Houthi missiles. Semafor. https://www.semafor.com/article/09/25/2026/saudi-arabia-intercepts-houthi-missiles
Holland, S., & Hafezi, P. (2026, 25 September). Trump rejects Iranian peace proposal, WSJ reports. Al-Monitor. https://www.al-monitor.com/originals/2026/09/allies-unite-behind-saudi-arabia-houthis-step-attacks
Lloyd’s List Intelligence. (2026, 3 September). Red Sea brief: 3 September 2026. https://www.lloydslistintelligence.com/resources/blog/red-sea-brief-3-september-2026
Lucente, A. (2026, 15 September). Houthi top diplomat says no intention to shut down Red Sea shipping, group open to talks. Al-Monitor. https://www.al-monitor.com/originals/2026/09/houthi-top-diplomat-says-no-intention-shut-down-red-sea-shipping-group-open-talks
Magdy, S., Fraser, S., & Ahmed, M. (2026, 16 September). Saudis seek allies’ help as missile defenses run low in fight with Houthis, officials say. The Atlanta Journal-Constitution. https://www.ajc.com/news/2026/09/saudis-seek-allies-help-as-missile-defenses-run-low-in-fight-with-houthis-officials-say/
Martinez, L. (2025, 21 November). New US-Saudi security deal raises questions. ABC News. https://www.goodmorningamerica.com/news/story/new-us-saudi-security-deal-raises-questions-127753446
Schuler, M. (2026, 22 September). Trump calls for Iran’s economic isolation at UN as Tehran offers Hormuz reopening. gCaptain. https://gcaptain.com/trump-calls-for-irans-economic-isolation-at-un-as-tehran-offers-hormuz-reopening/
Tang, S. (2009). The security dilemma: A conceptual analysis. Security Studies, 18(3), 587–623. https://doi.org/10.1080/09636410903133050
Tolba, A. (2026, 6 September). Four killed in Israeli strikes on southern Lebanon. Newcastle Herald. https://www.newcastleherald.com.au/story/9344706/israeli-strikes-lebanon-after-hezbollah-launched-drones/
Yap, T., Verma, N., & Tan, F. (2026, 22 September). Saudi Arabia restarts East-West oil pipeline, sources say. Al-Monitor. https://www.al-monitor.com/originals/2026/09/saudi-arabia-restarts-east-west-oil-pipeline-sources-say
Furkan Mahmut Tameroglu