As Donald Trump and Volodymyr Zelenskyy’s latest meeting reportedly descended into another shouting match, the war in Ukraine feels as volatile as ever - and, according to some, more dangerous for the world than at any time since the Cold War.In this episode of The Fourcast, Matt Frei is joined by Serhii Plokhy, professor of Ukrainian history at Harvard and author of The Nuclear Age. He warns that fear is once again driving nations towards the bomb - and that we could soon see dozens more nuclear-armed states. So is the world stumbling into a new nuclear era - and what does that mean for global security and for Ukraine’s fight to survive?