On the other hand, the school of catastrophic collapse holds that the fall of the Empire had not been a pre-determined event and need not be taken for granted. Rather, it was due to the combined effect of a number of adverse processes, many of them set in motion by the Migration of the Peoples, that together applied too much stress to the Empire's basically sound structure. Finally, the transformation school challenges the whole notion of the 'fall' of the Empire, asking to distinguish between the fall into disuse of a particular political dispensation, anyway unworkable towards its end, and the fate of the Roman civilisation which under-girded the Empire. According to this school, drawing its basic premise from the Pirenne thesis, the Roman world underwent a gradual (though often violent) series of transformations, morphing into the medieval world. The historians belonging to this school often prefer to speak of Late Antiquity instead of the Fall of the Roman Empire. In "The History of the Decline and Fall of the Roman Empire" (1776–88), Edward Gibbon famously placed the blame on a loss of civic virtue among the Roman citizens. They gradually entrusted the role of defending the Empire to barbarian mercenaries who eventually turned on them. Gibbon held that Christianity contributed to this shift by making the populace less interested in the worldly "here-and-now" because it was willing to wait for the rewards of heaven. Writing in the 5th century, the Roman historian Vegetius pleaded for reform of what must have been a greatly weakened army. The historian Arther Ferrill has suggested that the Roman Empire – particularly the military – declined largely as a result of an influx of Germanic mercenaries into the ranks of the legions. This "Germanization" and the resultant cultural dilution or "barbarization" led not only to a decline in the standard of drill and overall military preparedness within the Empire, but also to a decline of loyalty to the Roman government in favor of loyalty to commanders. Ferrill agrees with other Roman historians such as A.H.M. Jones: In contrast with the declining empire theories, historians such as Arnold J. Toynbee and James Burke argue that the Roman Empire itself was a rotten system from its inception, and that the entire Imperial era was one of steady decay of institutions founded in Republican times. In their view, the Empire could never have lasted longer than it did without radical reforms that no Emperor could implement. The Romans had no budgetary system and thus wasted whatever resources they had available.