James Mattis issued the warning to the other 27 members of the alliance on Wednesday during a closed session at Nato headquarters in Brussels on his first visit to Europe as a senior member of Donald Trump’s cabinet.
Mattis’s predecessors have made similar threats over the last decade during visits to Nato, but without the same conviction. “I owe it to you to give you clarity on the political reality in the United States, and to state the fair demand from my country’s people in concrete terms,” he said.
“America will meet its responsibilities, but if your nations do not want to see America moderate its commitment to this alliance, each of your capitals needs to show support for our common defence.”
Trump repeatedly said on the campaign trail last year that it was time for European countries to stump up a fair share for an organisation he denounced as “obsolete”. He created alarm among other Nato members when he said the US might not automatically come to the defence of a fellow member under attack.