The post-second world war taboo on acquiring territory through force or by the threat of force is being unravelled by a generation of political leaders, led by expansionist threats from Donald Trump that are unprecedented for a US president. Experts are warning that a combination of the Russian aggression against Ukraine and Trump’s comments explicitly pushing for the US to acquire Greenland, Canada, the Panama canal and Gaza is fuelling a permissive environment that threatens long-recognised borders and the international rules-based order that has existed since the end of the war. The norm, enshrined in article 2 of the UN...