The officers who pursued Napoleon into Western Europe brought ideas of liberalism back to Russia with them and attempted to curtail the tsar's powers during the abortive Decembrist revolt of 1825. At the end of the conservative reign of Nicholas I (1825–55), a zenith period of Russia's power and influence in Europe, was disrupted by defeat in the Crimean War. Between 1847 and 1851, around one million people died across the country due to cholera.