Donald’s Trump’s threat to “destroy North Korea”, which raised the spectre of nuclear war and murder and destruction on a scale unprecedented since World War Two, understandably dominated the headlines in the wake of his speech to the United Nations on 20 September.

But horrifying as this threat was, it is possible that what Trump said in this speech about Iran will prove to be its most long-lasting and damaging element:

“It is far past time for the nations of the world to confront another reckless regime – one that speaks openly of mass murder, vowing death to America, destruction to Israel and ruin for many leaders and nations in this room …

“We cannot let a murderous regime continue these destabilising activities while building dangerous missiles; and we cannot abide by an agreement if it provides cover for the eventual construction of a nuclear program. Frankly, that deal is an embarrassment to the United States, and I don’t think you’ve heard the last of it, believe me.”

Trump spent more time attacking Iran than he did North Korea. And his threat to tear up the Iran nuclear deal, negotiated by the Obama administration, increases the risk of conflict in the Middle East and beyond.

If the Iran deal is broken, there is every possibility that the multifaceted geopolitical struggle in the Middle East, which is primarily a conflict between Iran and Saudi Arabia, but also involves a number of other powers such as Turkey, will develop a nuclear aspect.

Iran would feel compelled to restart its nuclear weapons program at pace. This could provoke a US military response. Even if it didn’t, a nuclear Iran might provoke Saudi Arabia to buy nuclear weapons or develop its own nuclear program. Israel, which is already a nuclear power, could react in any number of ways that might increase the possibility of war.

But it is possible that the most disastrous impact of Trump’s threat to nullify the Iran deal will be felt on the Korean peninsula.

Trump’s threats against Iran send a clear message to North Korea: you can’t negotiate with the US. Even if you sign a comprehensive deal with the president, that deal can be annulled on a whim. If you don’t have a nuclear capacity, or if you agree to renounce nuclear weapons in return for diplomatic recognition, this will be used against you. The only real guarantee that the US will not attempt to overthrow your government is if you develop a nuclear weapons capacity that can obliterate US cities or the cities of its allies.

The North Korean nuclear program has been driven by the conviction that the examples of Iraq and Libya prove that a nuclear deterrent is the only way to prevent a US “regime change” operation in North Korea.

Trump’s latest threats against Iran only prove the accuracy of this thesis. That’s the message the US is sending to the world. Either you develop weapons that can kill millions of people, or we might kill millions of you.