The taboo on territorial conquest that kept a shaky peace for 85 years was first broken by Russia and now legitimised by the Trump administration. All countries will need to completely reevaluate their defence strategies in this new age of empires. If India looks dangerously reliant on Russian arms imports, for instance, shifting to Washington hardly appears to be a stable solution—while diversification of military imports can mitigate risk in the medium term, there is now no alternative to domestic production for every essential component of defence. It’s hard to predict what a “multipolar” world, in which territorial conquest is once again legitimate, will look like in the nuclear age. Ukraine provides a sketch of this future, with the largest nuclear power plant in Europe under Russian occupation in Zaporizhzhia and frequent Russian nuclear sabre-rattling that has at times been effective in miring Ukraine’s allies in paralysing “escalation management”. The UN system, international law and even the Geneva Convention have lost legitimacy as Russia has routinely executed and tortured Ukrainian captives and abducted tens of thousands of Ukrainian children. Despite an order for Putin’s arrest in The Hague on charges of genocide, not only has China declared an “unlimited friendship”, but Trump has embraced him as an equal partner that many in the Make America Great Again (MAGA) movement see as a model for a muscular, authoritarian response to liberalism. History has repeatedly demonstrated that a respect for the laws of war means the difference between devastation and relative order. In our new chaotic world, even the once unthinkable—a US invasion of Canada, for instance—now must be considered a possibility, with far-reaching geopolitical consequences.