"The question of deradicalization looms large in the historiography of western European socialism. But in this contested field, the contributions of the New Left historian, Ralph Miliband, have been curiously neglected. Through his work on the British Labour Party, Miliband developed a distinctive account of deradicalization that foregrounds the fact that when parties enter government, party elites find themselves transplanted into new, alien institutions. Over time, he argued, they then come to internalize the worldviews of those institutions and reshape their parties accordingly. This essay presents the first quantitative and cross-national test of this “experience of governing hypothesis,” using Comparative Manifesto Project data from western European socialist parties between 1945 and 2021 and a novel matching technique for panel data. Miliband's theory is strongly supported by this analysis, which also demonstrates the value of taking a multi-dimensional approach to deradicalization."

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