In November 1914, after the outbreak of the First World War, Stefan Zweig noted in his Diaries: "I had to write to Romain Rolland; I needed to unburden myself to a friend. No one here understands me: they lack the firm will to be fair." And it was precisely this heightened sense of justice, as well as his fervent defense of pacifism and humanist ideals, that united the future French Nobel Prize winner with his most faithful Austrian disciple. Both spoke out publicly against the war, denouncing in their letters fake news, hatred between nations, and the selfishness of those who remain silent. This correspondence, written by two kindred spirits from two warring countries, is an exceptional testimony to the catastrophe of the Great War and to the fervent desire of two of the most lucid writers of the first half of the 20th century to build a united Europe based on fraternity among peoples.