President Donald Trump’s unilateral decision to withdraw from the multilateral agreement to restrain Iran’s nuclear program will inevitably have far-reaching consequences, including the further destabilisation of the Middle East.

More immediately, it risks fracturing a Western alliance that has provided the cornerstone of global security since the end of the second world war.

In a joint statement, the leaders of France, Germany and Britain raised the possibility of the US being in breach of a United Nations Security Council resolution endorsing the deal. The resolution remained the “binding international legal framework for the resolution of the dispute,” Emmanuel Macron, Angela Merkel and Theresa May said.

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As such, France, Germany and Britain said they would still adhere to the agreement. The other participants – Russia and China – would also be unlikely to abandon the deal. And Iran itself, in a measured reaction to the Trump announcement, said it, too, would stick with the agreement.

This means the Trump administration risks finding itself further isolated from the international community, following his decision to also pull out of the Trans-Pacific Partnership and the Paris Climate Change accords.

Possible ramifications

It is hard to exaggerate the many negative outcomes that may well flow from the decision to pull out of the Iran nuclear deal, including an escalation of tensions between Iran and US clients in the Middle East. In fact, heightened tensions across the Middle East and an intensification of a regional arms race would seem to be almost inevitable.

Following through on his threats during his 2016 presidential election campaign to tear up the Iran deal, Trump could hardly have been more explicit in his rejection of a foreign policy centrepiece of his predecessor’s tenure in his announcement on Tuesday.

The fact is, this was a horrible, one-sided deal that should have never, ever been made. It didn’t bring calm, it didn’t bring peace, and it never will.

What this announcement confirms – if confirmation is even necessary – is that the US leader has unshackled himself from the moderating influences of advisers who have been shoved out of his national security team in recent weeks. These include Harold McMaster, his former national security adviser, and former Secretary of State Rex Tillerson, who had both argued strenuously against a withdrawal from the Iran deal.

Trump is now in the hands of what is one of the more bellicose teams of advisers assembled by an American president in recent memory. Where this leaves James Mattis, Trump’s defence secretary is unclear. Mattis has called the verification element of the Iran deal “robust” and has been opposed to actions that would undermine an existing treaty.

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Read more: Donald Trump backs out of Iran nuclear deal: now what?

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Understandably, former President Barack Obama and his secretary of state, John Kerry, have expressed dismay over an unravelling of an agreement that took years to negotiate with the aim of forestalling Iran’s acquisition of a nuclear weapons.

In a rare rebuke of Trump, Obama said the decision would make the world less safe. He described it as a “losing choice between a nuclear-armed Iran or another war in the Middle East.”

Understandably - as one of the architects of the agreement - Kerry also expressed his dismay. “Instead of building on unprecedented nonproliferation verification measures, this decision risks throwing them away and dragging the world back to the brink we faced a few years ago,” he said.

Possible impact on business

In addition to tearing up the deal, Trump announced a re-imposition – and strengthening – of sanctions against Iran. These will be phased in over 90-day and 180-day periods. What is not clear is what impact these sanctions will have on international companies doing business in Iran.

Under a previous sanctions regime, companies risked being shut out of the US economy if they invested in – or traded with – Iran.

An interpretation of just what is implied for international business will be an early test of America’s ability to make the sanctions stick. This is sure to get messy.

Already, US companies such as Boeing, which had negotiated US$20 billion in aircraft sales to Iran, are finding such business is now in jeopardy.

Further complicating the picture is Trump’s proposed face-to-face meeting with North Korean leader Kim Jong-un to put an end to Pyongyang’s nuclear program.

Kim may well ask himself what value might be placed on negotiations with Trump. Under these circumstances, neither side would be likely to invest much trust in one another.

Tony Walker does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.