The trajectories of power of political aristocrats demonstrate how their constitutive values were defined in relation to the empire, placing the guiding principle of ‘imperial unity’ as the utmost priority in the conduct of European politics. This dissertation looks at the public lives of four political aristocrats from three different empires – Britain, Austria and Russia – from c.1820-1870, in order to examine the evolution of the principle of ‘imperial unity’ amidst cultural re-evaluations with significant implications for the direction of the state-building project. Special attention is dedicated to the period after the Crimean War (1853-1856), inaugurating a transformative decade. The ‘post-war mentality’ embedded in the political aristocracy during the 1860s led to coordinated responses, more than reactions, to the external and internal challenges to the empire and its unity, creating an extraordinary moment of deliberate state-building (through reform, but also war and/or imperial compromise/mediation). The threats posed to imperial unity by the Crimean War and its outcomes produced a sense of imperial vulnerability among leading political aristocrats that ultimately changed the way they envisioned empire-maintenance. This ‘post-war mentality,’ I argue, laid the grounds for substantial political innovation, because the sense of vulnerability deriving fromthe experiences of war compelled political aristocrats to diversify the strategies of imperial unity. From military intervention and conflict to policymaking and institution strengthening, the diversification of these strategies raised novel (yet predominantly aristocratic) notions of ‘good governance’ aimed at legitimising the post-(Crimean-) war empire through progress. The 1860s presented a unique interpretational frame for internal and external politics vis-à-vis the principle of imperial unity, which would prove crucial for consolidating the role of political aristocrats both as guardians of the empire and as agents of change.