When studying history in school, and even university, 'history' is divided into distinct era's or periods, such as the Roman Empire, Dark Ages, Middle-Ages, etc. Each of these periods has a distinct characteristic or theme about them. I find myself looking at the roman empire and then early medieval Europe and wondering 'how did one period transition into another?' Are there any good books that map out the history of Europe in the transition from the roman empire to what became medieval Europe? As in, something that explains and describes the process of the fall of the roman empire and the creation of christian medieval, feudal kingdoms? thanks