THIS week, Nato marks the 75th anniversary of the signing of its founding treaty, yet the mood music is far from celebratory. Key leaders within the military alliance are increasingly concerned that the bloc is facing its biggest ever challenges.

Take the example of Polish Prime Minister Donald Tusk, a former European Council president, who warned last week that Europe is in a dangerous, new “pre-war era”. He asserted that Ukraine must not be defeated by Russia for the good not just of Nato members but all nations that value the post-1945 rules-based order.

Tusk said that war is “no longer a concept from the past”, that “it’s real”, and that “literally any scenario is now possible”.