One of the classical questions in the study of nationalism concerns the end of empires. Is nationalism, to use the phrase of Hiers and Wimmer, the cause or consequence of the end of empire? This paper considers a neglected case, that of the decomposition of the Danish imperial monarchy in the years between 1848 and 1864. We find that nationalist conflicts indisputably caused the end of this political entity. Crucially, Danish nationalists in the imperial core preferred to downsize the territories controlled by the Oldenburgs rather than to share power with German speakers in the periphery. Decomposition was not, however, inevitable: an early introduction of power-sharing schemes might have saved the imperial monarchy.