Fixed smiles will doubtless be in place for the traditional "family photograph" when Nato leaders meet outside London later for a three-hour formal meeting covering issues such as cyber-attacks and the strategic challenge posed by China. But at the highly choreographed gathering, intended to celebrate the defence alliance's 70th anniversary, there is no hiding the deep differences between members. While Prime Minister Boris Johnson, as host, is expected to highlight members' commitment to defend one another under a principle of "one for all, and all for one", US President Donald Trump criticised French President Emmanuel Macron's questioning of American commitment to the alliance. He said Mr Macron had been "very disrespectful" and said his description of Nato as "brain-dead" was "nasty". 

As our video explains, disputes continue over members' commitment to funding the alliance and Turkey's fight against Kurdish groups it considers terrorists but who were allies of other Nato members in Syria. Both topics were discussed when Mr Johnson hosted an "off-camera, one-to-one meeting" with Mr Trump in No 10 during a reception for world leaders, Downing Street says. The US president had earlier touched on the UK election by saying he could "work with any prime minister".

If you're confused about what Nato does, check out our profile. Meanwhile, our Reality Check team analyses what the US does for the alliance.

Fixed smiles will doubtless be in place for the traditional "family photograph" when Nato leaders meet outside London later for a three-hour formal meeting covering issues such as cyber-attacks and the strategic challenge posed by China. But at the highly choreographed gathering, intended to celebrate the defence alliance's 70th anniversary, there is no hiding the deep differences between members. While Prime Minister Boris Johnson, as host, is expected to highlight members' commitment to defend one another under a principle of "one for all, and all for one", US President Donald Trump criticised French President Emmanuel Macron's questioning of American commitment to the alliance. He said Mr Macron had been "very disrespectful" and said his description of Nato as "brain-dead" was "nasty". 

As our video explains, disputes continue over members' commitment to funding the alliance and Turkey's fight against Kurdish groups it considers terrorists but who were allies of other Nato members in Syria. Both topics were discussed when Mr Johnson hosted an "off-camera, one-to-one meeting" with Mr Trump in No 10 during a reception for world leaders, Downing Street says. The US president had earlier touched on the UK election by saying he could "work with any prime minister".

If you're confused about what Nato does, check out our profile. Meanwhile, our Reality Check team analyses what the US does for the alliance.