Rome’s decline occurred roughly from 200 to 500 CE, during which an empire that seemed indomitable saw its end at the hands of less powerful peoples. These 300 years encompassed a shift from Roman order to bloody and lawless disorder, far worse than any of the revolts, military difficulties, and economic downturns of the Republic or the early Empire. By Constantine's time, the foundations for Medieval Europe were already being laid. Various tribes were encroaching on the Empire’s lands, emperors became more like absolutist kings, peasants involuntarily labored on lands not their own, personal law began to replace the impersonal law common to large territories, and the Catholic Church began to rise in power.
However, the factors that led to Rome’s decline were not new; they were simply aggravations of preexisting conditions. The external pressures the Empire faced from encroaching tribes uncovered its internal difficulties, weakening its hold on its vast lands. Roman military responses to upsets within the Empire had historically been far too weak initially, costing the empire far more time and manpower to clean up the mess they had made than if they had responded strongly in the first place. Domestically speaking, the problem of succession had been apparent to all from before the time of Caesar. The Empire’s size was another issue. It was too big, and the lanes of communication—in military, food supply, and cultural terms—were far too inefficient.
In addition, Rome was plagued by a struggle that had defined much of ancient and pre-modern history: conflict between settled, sedentary, agrarian societies and nomadic, pastoral, raiding cultures. The two had never been able to coexist successfully, and Rome would be no exception to this rule. The nomadic tribes surrounding Rome were attracted to the materials of the settled civilization, as well as its culture, leading to increased nomadic incursions over the long term.
Finally, it is important to remember how disunified Rome was. Despite its vast reach, not all living within Roman borders were Romanized in culture, language, and politics. There was often a clear divide between the more Roman political elites, political structures, and cultural elites, and the diverse masses, which of course outnumbered the elites. However, despite this, even after the western Empire’s demise in 476, Roman forms of organization in state and society persisted. Not only did native Roman leaders and local administrators try to keep up cultural appearances, but the tribal peoples entering Roman lands also enthusiastically tried to maintain what they thought Rome was. Future leaders would maintain Roman political hierarchies, the Latin language, Roman architecture, even a relationship with the Eastern Roman Emperor.