Through a study of British historical writing during the last decades of the nineteenth century, and of US historical and political writing after the 9/11 terror attacks, this paper proposes that Empire tends to become visible to the imperial metropolis in moments of imperial crisis. While Empire is always apparent to the colonized, it appears in the metropolis primarily as a resource described through economic language, and it is not necessarily made visible as a global political institution. When Empire is threatened, however, it does become visible as something also political and historical. It is when the barbarians are understood to be standing at the door, that Empire becomes so important that the metropole begins to theorize it. In doing so, nostalgia becomes an important tool to Empire, a plea to the citizens of the metropole to imagine the past of the Empire as idyllic, and to think of themselves as deeply vested in this idyllic past. Such an emotional engagement with an imagined past is useful, the paper concludes, if a society is to send their young men and women to war, to forgo civil liberties, and to accept the dismantling of welfare structures.