Nato leaders met outside of London for formal talks to mark the 70th anniversary of the military alliance on Wednesday amid public infighting between member states.
Welcoming leaders to the summit, British Prime Minister Boris Johnson said: "As long as we stand together, no one can hope to defeat us."
There have been disagreements over the amount of military spending by members, the recent Turkish offensive into Kurdish-held areas in Syria and French President Emmanuel Macron describing the alliance as "brain dead".
Mr Macron was asked on Wednesday as he arrived for the talks at the Grove Hotel, north-east of London, whether he stood by his comments.
"Yes, absolutely. In fact it allowed us to raise some crucial debates," he said.
After the three-hour talks, Nato Secretary Jens Stoltenberg played down differences between the allies.
He said the alliance had agreed to start a "meaningful dialogue" with Russia, to encourage China to participate in arms control, and that Turkey had dropped its opposition to bolstering defences of Baltic states and Poland.
But he said the issue of the Syrian Kurdish YPG militia, which Turkey views as a terrorist organisation, was not discussed during the Atlantic Council session.
“It was not addressed specifically in the meeting today,” he said.
The alliance had remained united on the core issues, Mr Stoltenberg said.
“We all agree on the importance of not jeopardising the gains we have made in the fight against terrorism.”
Mr Stoltenberg said that European allies and Canada have increased their defence budgets by $130 billion since 2016.
The US has complained that fellow Nato members were not pulling their weight when it came to military spending.
“This is unprecedented, this is making us stronger,” Mr Stoltenberg added.
On the first day of the summit on Tuesday, US President Donald Trump described Mr Macron’s comments about Nato as “insulting” and “nasty”, before the pair sparred in front of TV cameras over foreign ISIS fighters in Syria.
Mr Trump said France and other European nations needed to be spending 4 per cent of their annual GDP on national defence by 2024, rather than the pledge of 2 per cent.
“You could make the case that they’ve been delinquent for 25-30 years,” he said.
While the leaders appeared to be in good spirits at an official reception at Buckingham Palace, a video published to social media appeared to show Mr Macron, Canada’s Justin Trudeau and Mr Johnson mocking Mr Trump.
"Is that why you were late?" Mr Johnson asked Mr Macron.
"He was late because he takes a 40-minute press conference off the top," Mr Trudeau responds, apparently referring to the US President's unscheduled 40-minute question and answer session.
"You just watched his team's jaws drop to the floor."
Mr Trump retaliated against Mr Trudeau later on Wednesday.
"He's two-faced," he said. "I find him to be a very nice guy but you know the truth is that I called him out on the fact that he's not paying 2 per cent and I can see he's not very happy about it.
"He's not paying 2 per cent and he should be paying 2 per cent. Canada – they have money."
The US president cancelled his press conference and flew back to Washington, saying on Twitter that "great progress" had been made by Nato over the past three years.
Mr Johnson was accused of not taking Mr Trump seriously.
"That's complete nonsense and I don't know where that has come from," he said.
Asked about the video, Mr Johnson said he knew nothing about it.
It appeared he was doing all he could to publicly distance himself from the Mr Trump by holding talks with him in private and not posing for a photograph afterwards.
The US president is unpopular in the UK and Mr Johnson did not want to harm his chances days before a general election.
"We had a very good meeting and we discussed the future of Nato, what is going on in Syria and various other security matters," he said when arriving for the talks on Wednesday.
Mr Johnson said he wanted to pose for a photograph with all of the Nato leaders.
After the meeting, the leaders published a declaration underlining their commitment to Nato, declaring unity against cyber threats and terrorism in all its forms.