France should be “prepared to lose children.” With those words, spoken on November 18, 2025, before France’s mayors gathered at the Porte de Versailles in Paris, General Fabien Mandon, chief of the General Staff of the Armed Forces, left many in the audience stunned. Suddenly, the thud of bombings in Ukraine felt much closer. A “clash” between Russian forces and the French army could possibly occur, he warned, “in three or four years.” His remarks sparked controversy but also a moment of realization. Yes, war could return to Western Europe, bringing with it suffering and lives cut short. The idea that we are not shielded from such violence seems absurd and senseless. But it is no longer unthinkable. And now, everyone is once again faced with a question that seems naive, but is, in fact, both wrenching and metaphysical: Why war?

Two of the greatest minds in history set out to answer this question in the early 1930s: Albert Einstein and Sigmund Freud. The acrid memory of the Great War still lingered over Europe. As today, everything seemed bleak. The global economic crisis was battering democracies, and people doubted their ability to cope. Benito Mussolini was consolidating his power in Italy. In Germany, humiliated by the terms of the Treaty of Versailles, economic and political instability paved the way for the rise of Adolf Hitler’s Nazi Party. It was in this grim atmosphere that the International Institute of Intellectual Cooperation – a forerunner of UNESCO, created under the aegis of the newly formed League of Nations, to promote scientific and cultural dialogue – invited Einstein to open a correspondence with a person of his choice on the theme of war. Could humanity ever be freed from it?

At 53, Einstein was spending his last few months in Berlin. Attacked from all sides by the antisemitic far right in his country, he would leave Germany for good at the end of 1932. Widely regarded as the greatest living scientist, he published his theory of general relativity in 1915 and received the Nobel Prize in Physics six years later for his explanation of the photoelectric effect. He chose to write to the Austrian Freud, who was 22 years his senior. These two giants had each discovered a new continent – relativity and the unconscious. They barely knew each other. They had crossed paths only once, at the end of 1926, in Berlin, at the home of the psychoanalyst’s son, Ernst. Freud recounted the meeting a few days later in a letter to his friend Sandor Ferenczi: “He [Einstein] is cheerful, confident and kind, understands as much about psychology as I do about physics, and so we had a very good conversation.” For his part, the physicist doubted the psychoanalyst’s theories, but he respected his “powerful influence on our contemporary view of the world,” as he would later write. A few months after their 1926 meeting, he declined the idea of undergoing psychoanalysis on Freud’s couch: “I should like very much to remain in the darkness of not having been analyzed.”

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