Get you up to speed: Trump has plunged the Middle East into a conflict that may last for weeks.

What we know so far

Donald Trump has rolled the dice again, stunning the world by choosing the most extreme option over Iran.

His decision to attack and try and topple Iran’s regime with the backing of Israel tips the Middle East into a massive war that could last weeks.

By the end of last week, the stage had been set for more diplomacy. Talks in Geneva had been making some progress and more were planned for Monday.

Iran strikes US military base in Bahrain

That appears to have been a ruse, to lull the enemy into thinking an attack was not imminent.

Mr. Trump has unleashed American military force without either the approval of the UN or the US Congress.

There has been no pretence at securing even a fig leaf of justification under international law.

He had been urged by allies in the region, apart from Israel, to avoid war.

If it leads to the end of the ayatollahs’ regime, there will be jubilation among them, but that is a very big if.

Iran had warned it would take the gloves off if attacked and will most likely do just that, its leadership seeing this as a fight for survival.

There are already reports of attacks on countries and installations across the Persian Gulf.

It is a seaway through which a fifth of the world’s oil passes, so a sustained conflict is likely to have major repercussions on the global economy.

The American-Israeli offensive poses a dilemma for Britain.

Prime Minister Sir Keir Starmer, worried about the implications under international law, has ruled out British bases being used to support the assault on Iran.

There will be severe misgivings at the highest level of government here about the wisdom and legality of this unprecedented move by Britain’s closest ally but there will also be a determination that it does not damage transatlantic relations.

And there will be the suspicion that this has been motivated more by Donald Trump’s deepening domestic woes than by sound military thinking.

He faces an affordability crisis back home and continuing pressure over the Epstein scandal.

This is a massive gamble by an American president whose popularity is plummeting.

He has set the objective high, hoping to sufficiently damage Iran’s regime so that its people can rise up and take over.

Anything short of that may be seen as an expensive failure, which could prove very costly for Mr. Trump in the run-up to this year’s vital US mid-term elections.