US–Iran ceasefire: What it means for Trump, Tehran, Israel and US allies. Early analysis from Chatham House experts

US–Iran ceasefire: What it means for Trump, Tehran, Israel and US allies. Early analysis from Chatham House experts

US–Iran ceasefire: What it means for Trump, Tehran, Israel and US allies. Early analysis from Chatham House experts Expert comment jon.wallace 8 April 2026 What does the ceasefire mean for the Islamic Republic, President Trump, the Strait of Hormuz and the UK? And how should the world respond to challenges to the humanitarian legal order? The US, Israel and Iran announced a ceasefire on 7 April, leading to an end to attacks by each side and the reopening of the Strait of Hormuz. The announcement came shortly before a deadline set by US President Donald Trump for Iran to reopen the Strait. The president had previously threatened to bomb Iran ‘into the Stone Ages’ and destroy its ‘whole civilization’ if it did not comply. Both Washington and Tehran hailed the ceasefire, negotiated by Pakistan, as a victory. Israeli Prime Minister Benjamin Netanyahu said the ceasefire did not apply to Israel’s operations in Lebanon. Here Chatham House experts provide their early analysis on the implications of the ceasefire, for the US, the region and the world. Dr Sanam Vakil on how difficult issues remain Professor Marc Weller on the credibility of international law Dr Marion Messmer on US strategic mistakes Olivia O’Sullivan on hard choices facing the UK Dr Sanam Vakil, Director of the Middle East and North Africa Programme: The ceasefire will be welcomed as a necessary step back from the brink after days of escalating strikes, mounting threats against Iranian and Gulf infrastructure, and continued disruption to shipping through the Strait of Hormuz. All of these elements underscored that this had become a war that no side was clearly winning and in which the costs were rising faster than any achievable gains. The most difficult issues will now have to be worked through in detail by negotiators in Islamabad: Can the United States offer credible assurances against renewed strikes and be trusted to uphold them? And is Iran willing to accept limits on its ability to threaten shipping in the Strait? Crucial to a lasting agreement is that Tehran demonstrates a willingness to compromise on its nuclear programme, through for instance a new inspection regime. Equally important is that Washington is willing to structure sanctions relief in a way that makes de-escalation politically sustainable on both sides. There remains a real possibility that tensions could resurface, whether through further threats, resumed pressure on the Strait, or the need to extend negotiations. Meanwhile, there is a real risk that regional considerations are sidelined. Iran has pushed for the ceasefire to extend to Lebanon, viewing the conflict there as part of the same confrontation. Yet Israel has made clear that its campaign against Hezbollah is not covered by the truce and is prepared to continue operations. Gulf states, meanwhile, are seeking assurances that they will not remain exposed to repeated pressure on their infrastructure and shipping routes. Israel remains deeply sceptical of any arrangement that leaves Iran’s missile, nuclear and regional capabilities intact. These are difficult issues that will not be easily resolved in a matter of weeks. With US forces still building up in the region and the risk of renewed escalation never far away, there remains a real possibility that tensions could resurface, whether through further threats, resumed pressure on the Strait, or the need to extend negotiations beyond their initial timeframe. If the talks in Islamabad focus too narrowly on American and Iranian priorities, they may succeed in stabilizing the immediate crisis while leaving the broader regional order fragile – and exposed to revived escalation. Professor Marc Weller, Director of the Global Governance and Security Centre: This ceasefire has been obtained under the threat of a massive attack against Iran’s civilian infrastructure. US President Donald Trump threatened to bomb Iran ‘back to the Stone Ages’ and to permanently erase its civilization. This may have been a further example of bluster and brinkmanship on the part of the president. Yet the threats raise further, profound questions about the credibility of international law as a tool of constraining the most powerful countries. US service-members and their commanding authorities who carried out the president’s threats would have exposed themselves to allegations of grave breaches of the law of armed conflict – although Iran, Israel and the US are not subject to the jurisdiction of the International Criminal Court at The Hague. Crucially, international law develops through the practice of states. When states violate key tenets of the law, or credibly threaten to do so, it is the response of the rest of the world that decides whether this will create a new pattern of practice going against the established rules. In this instance, once again, there was no immediate chorus of condemnation from other countries in reply to President Trump’s threats, even as they challenged the humanitarian legal order at its core. It was left to Pope Leo XIV, an American, to speak out, declaring the threats against the people of Iran ‘unacceptable’. The world will need to learn to resist such challenges to the legal order, if it does not want to awake one day in a lawless and dangerous world where others routinely copy such behaviour. Meanwhile, serious immediate challenges to international law remain: Iran has shown it has the ability to choke off some 20 per cent of the global oil supply by blocking the Strait of Hormuz. However, instead of fully opening the Strait in exchange for the ceasefire, it insists, at least for now, on maintaining its control. That leaves the risk that Iran may continue to exclude ‘unfriendly’ flag states from passage through the Strait and subject others to inspections, delays and exorbitant fees. Dr Marion Messmer, Director of the International Security Programme The agreed ceasefire between the US and Iran is a welcome reprieve for the Middle East and the global community. But overall the US action has not provided the display of strength the Trump administration hoped for. It has depleted US ammunition stockpiles in the Middle East and shown the limits of existing US capabilities in terms of being able to intercept missiles and drones, as well as the extent to which the US does not have scalable and affordable anti-drone defences in place at its military bases. The US has also made a series of serious strategic mistakes: it has overestimated the role of air power in being able to effect regime change and drive outcomes and underappreciated Iran’s organisational and military resilience. The US use of force has undermined international law and the international order. The Trump administration threatened European allies that did not want to involve themselves in a war of choice by saying that the US might leave NATO, and it raised concerns among Asian allies by moving missile defence equipment to the Middle East. It is doubtful that this was worth the costs to US military capability, and more importantly, to US relationships and credibility. This has further undermined the credibility of US security guarantees, which will be difficult to recover and may further fuel proliferation dynamics. Furthermore, Israel’s insistence that its military action in Lebanon is not part of the agreement reveals a key vulnerability and shows the limits of the US ability to manage its allies: the ongoing bombing campaigns in Lebanon could undermine the ceasefire overall and keep the US trapped in a conflict it is now seeking to exit. After weeks of President Trump being furious with European allies for not sufficiently supporting the US, it now appears to be the alliance relationship with Israel that provides more of a risk to US interests in the Middle East. The 10-point peace plan published by the Iranian government also includes several points that the US has previously rejected, such as ongoing Iranian control over the Strait of Hormuz, and a US military withdrawal from the Middle East. It seems difficult to believe that the US can agree to these points and still declare a victory. While President Trump is celebrating the ceasefire as a US victory, it is looking likely that even the most successful outcome of the negotiations would only be a moderate improvement on the status quo before the war. It is doubtful that this was worth the costs to US military capability, and more importantly, to US relationships and credibility. Olivia O’Sullivan, Director of the UK in the World Programme Prime Minister Keir Starmer rightly called the temporary ceasefire agreed between the US and Iran a ‘moment of relief’. The reprieve is welcome, but a conclusive resolution remains out of reach. Iranian proposals for a long-term peace agreement still reportedly include demands the US will find difficult to accept, from Iran controlling or imposing tolls on the Strait of Hormuz, to sanctions on Iran being lifted. Starmer’s government will continue to be pulled into efforts to resolve the crisis. But they will also need to confront deeper questions about the UK’s alliance with the US – while planning for the likely prolonged economic effects of the war. Immediately, this is likely to mean continued regional diplomacy. Starmer has travelled to the Gulf on Wednesday to meet regional leaders. And the UK held a meeting of more than 40 countries last week to discuss ways to reopen the Strait of Hormuz. For the UK, these efforts are intended to manage the effects of the crisis and signal to the US and others it is playing a crucial role. But they are also an exercise in building coalitions with countries who badly need basic international norms – including principles on the use of force and freedom of navigation through international waterways – to hold. In the longer term, the crisis will create new urgency in defence and security cooperation with European nations and with the EU. The Trump administration’s erratic behaviour is making the kind of default Atlanticism that has driven UK foreign policy for decades less and less tenable. Decisions about whether to allow the US to use UK bases during the conflict have split UK political debate. And the question of how to build a defence and security architecture which is less dependent on the US has grown more urgent. For now, Starmer’s cautious position – allowing the use of bases by the US for defensive purposes but not offensive ones – seeks to carefully distance the UK from the conflict while recognizing it still has fundamental interests in defending regional allies, UK bases, and international shipping from the actions of Iran. In the longer term, the crisis will create new urgency in defence and security cooperation with European nations and with the EU. It should also force greater honesty with the public about the defence spending and planning needed to deal with a world where the UK’s principal defence partner has become unpredictable – and where basic security and diplomatic norms are becoming fragile. But the potential price shocks at home – from immediate fuel shortages and damage to critical shipping infrastructure in the region – may make exactly these decisions harder to sell to a weary public. Starmer has seen a very small uptick in his approval ratings during the course of the war – he will need to cling onto that momentum to manage its consequences. Chatham House experts will continue to provide analysis of developments in the conflict and the ceasefire in the coming days and weeks. Read more of our coverage of Iran and the Middle East.