British Prime Minister Keir Starmer has declared a “coalition of the willing” would come together to draw up a peace plan to end the war in Ukraine and present it to United States President Donald Trump for his support, days after a public spat between Trump and Ukrainian President Volodymyr Zelenskyy at the White House signalled a rupture in Washington’s support for Kyiv.

By contrast, Zelenskyy received assurances of support on Sunday from his European allies at a security summit in London hurriedly arranged by Starmer, who greeted the Ukrainian leader with a hug.

On Friday, a meeting between Trump and Zelenskyy soured quickly as it was broadcast live. An argument erupted with Trump repeatedly cutting off Zelenskyy and accusing him of “gambling with World War III”.

The Oval Office tensions followed a war of words between Trump and Zelenskyy, who cut his visit to the US short and promptly turned to Europe.

But what is a “coalition of the willing”, who might be part of it and can it meaningfully help Ukraine without US backing?

What did Starmer say?

After the security summit, Starmer said participants had agreed on four points:

• European leaders are willing to join forces and devise a peace plan for Ukraine to present to the US. “This is not a moment for more talk. It’s time to act, time to step up and lead and to unite around a new plan for a just and enduring peace,” the United Kingdom leader said.
• Any lasting peace effort must uphold Ukraine’s sovereignty, and Ukraine needs to be at the negotiating table.
• Starmer and other European leaders pledged to continue the flow of military aid to Ukraine.
• If a peace deal is reached, Ukraine’s defence capabilities will be bolstered. “In the event of a peace deal, we will keep boosting Ukraine’s own defensive capabilities to deter any future invasions,” the British prime minister said.

Starmer also announced a new 1.6-billion-pound ($2bn) deal with Ukraine on Sunday, which will allow Kyiv to spend the amount in export finance on 5,000 air defence missiles.

What is a coalition of the willing?

A coalition of the willing refers to a temporary international partnership created to resolve a specific issue or achieve a particular military or political goal.

The coalition that Starmer announced appears to have as its first task the formation of a plan to end the war in Ukraine that offers security guarantees to Kyiv but is palatable to Trump – who has made it clear that the US or NATO will not offer any such security umbrella.

It is unclear whether Starmer also meant that the coalition would take charge of implementing future security guarantees or whether member states would put boots on the ground in Ukraine for this.

Unlike a binding international body like the European Union or NATO, a coalition of the willing comprises countries who voluntarily or willingly join in.

European leaders have not divulged details of what this peace plan would entail. Before the summit, French President Emmanuel Macron told Le Figaro newspaper that the UK and France want to propose a one-month ceasefire pausing sea and air attacks as well as attacks on energy infrastructure. France and the UK have also indicated they are open to sending peacekeeping forces to Ukraine as part of any ceasefire.

Who is part of the coalition?

Starmer announced that the UK, France and other countries will join the coalition without specifying which other countries.

However, on Sunday, leaders or representatives of 12 European nations joined Starmer at the security summit in London. They were: Zelenskyy, Macron, Dutch Prime Minister Dick Schoof, Czech Prime Minister Petr Fiala, German Chancellor Olaf Scholz, Danish Prime Minister Mette Frederiksen, Swedish Prime Minister Ulf Kristersson, Norwegian Prime Minister Jonas Gahr Store, Finnish President Alexander Stubb, Italian Prime Minister Giorgia Meloni, Spanish Prime Minister Pedro Sanchez and Polish Prime Minister Donald Tusk.

European Commission President Ursula von der Leyen, European Council President Antonio Costa, outgoing Canadian Prime Minister Justin Trudeau, Turkish Foreign Minister Hakan Fidan and NATO Secretary-General Mark Rutte were also at the summit.

What prompted Starmer’s announcement?

The announcement was “obviously because of what happened in the White House on Friday”, Timothy Ash, an associate fellow in the Russia and Eurasia programme at Chatham House, told Al Jazeera. “Europe needed to step up in terms of the peace process, and it did.”

He added that it makes sense for Starmer to step up as the natural leader in the situation because the UK is not part of the EU and is a bridge between the US and Europe.

The EU as a whole is hobbled in its efforts to support Ukraine by the presence of Hungary, whose prime minister, Viktor Orban, has long resisted supporting Kyiv unconditionally.

In a letter to Costa on Saturday, Orban proposed that the EU should start direct discussions with Russia. “I am convinced that the European Union – following the example of the United States – should enter into direct discussions with Russia on a ceasefire and sustainable peace in Ukraine,” he wrote. “Therefore, I propose not to attempt adopting written conclusions on Ukraine.”

Will Starmer’s push help Ukraine?

Ash said Starmer’s recent moves were a “good thing” because Europe and Ukraine were not involved during earlier peace negotiations between the US and Russia in Saudi Arabia. “They should have been, and now they are.”

After leaving London, Zelenskyy said he had left with “Europe’s clear support”.

“The problem with the US-Russia peace process is that it wasn’t likely to be very durable,” Ash said. For it to be sustained, “the deal has to ensure that Ukraine continues to get the weapons it needs. This is more important than peacekeepers on the ground,” Ash said. He noted that the continued flow of weapons to Ukraine was not a point of discussion during the US-Russia peace talks.

Have there been such coalitions in the past?

Yes. In 1999, an Australia-led International Force East Timor (INTERFET) under a United Nations mandate and made up of soldiers from Australia, the UK and New Zealand landed in East Timor. This marked the first time the UN greenlit a peace mission by a coalition of the willing.

In 2003, 30 countries in some capacity provided support to former US President George W Bush’s invasion of Iraq, which did not have a UN mandate. These countries contributed to the invasion forces, which totalled about 160,000 soldiers. The UK contributed 45,000, and Australia sent about 2,000. The number of countries in the coalition grew to 38 after the invasion.

Can a coalition of the willing work without the US at its heart?

While the coalition can come up with a peace plan, both Zelenskyy and Starmer have acknowledged that they need US backing for the execution of a potential peace plan.

Zelenskyy said during one of his nightly video addresses: “There will be diplomacy for the sake of peace,” adding it will be “for the sake of us all being together – Ukraine, all of Europe and definitely, definitely America”.

“To support peace in our continent and to succeed, this effort must have strong US backing,” Starmer said after the summit.