LONDON — Britain and France have promised to muster a “coalition of the willing” to secure a peace agreement between Ukraine and Russia. Now comes the acid test for Europe: How many countries will step up, and does that even matter, given Russia’s rejection of such a coalition as part of any settlement?

Prime Minister Keir Starmer of Britain left those questions unanswered as he bade farewell to fellow leaders after a summit in London on Sunday. He conceded that “not every nation will feel able to contribute,” though he expressed optimism that several would, and that this would send a signal to President Donald Trump that Europe was ready to “do the heavy lifting.”

Drawing Trump back into the process is as important as the mission and scope of a European coalition, analysts say. For the moment, the United States appears determined to strike a deal with President Vladimir Putin of Russia over the heads of Europe and Ukraine, and without any security guarantees.

Starmer presented his coalition of the willing as one of multiple steps that included continued military aid for Ukraine to improve its position on the battlefield, a seat at the table for Ukraine in any peace negotiation and further help with its defensive capabilities after a settlement. That is where the coalition would come in.

In addition to Britain and France, northern European countries like Denmark and the Netherlands seem obvious candidates to take part. Both have been strong financial supporters of Ukraine’s war effort and are NATO members who contributed to other security campaigns, like that in Afghanistan. Germany is the second-largest contributor of military and other aid to Ukraine, after the United States.

But each country faces political and economic hurdles, such as the need to pass specific parliamentary measures in the Netherlands and the lack of a new government in Germany after recent elections. Denmark’s prime minister, Mette Frederiksen, said she had an “open mind.” Dick Schoof, prime minister of the Netherlands, said he had not yet made concrete commitments.

“We will renegotiate precisely these issues,” departing German Chancellor Olaf Scholz said after Sunday’s meeting, in what sounded like something less than a stirring call to arms. Ramping up military spending, he added, “will require an effort that many are not yet really sufficiently prepared for.”

Scholz’s likely successor, Friedrich Merz, is scrambling to obtain a huge amount of funding for defense — potentially at least 200 billion euros (about $207 billion) — in the current German parliament because he faces the prospect of an opposition minority in the next that is big enough to block additional spending.

President Emmanuel Macron of France said the nascent British-French plan would begin with a one-month truce between Ukraine and Russia. Any deployment of peacekeeping troops would come only after that, he said in an interview with French paper Le Figaro on Sunday evening.