Medieval history begins with the dissolution of the Western Empire, with the abandonment of the Latin world to German conquerors. Of the provinces affected by the catastrophe the youngest was Britain; and even Britain had then been Roman soil for more than three hundred years. For Italy, Spain, and Gaul, the change of masters meant the atrophy of institutions which, at first reluctantly accepted, had come by lapse of time to be accepted as part of the natural order. Large tracts of Europe lay outside the evacuated provinces; for the Romans never entered Ireland or Scandinavia or Russia, and had failed to subjugate Scotland and the greater part of modern Germany. But the Romanised provinces long remained the dominant force in European history; the hearth-fire of medieval culture was kindled on the ruins of the Empire. How far the victorious Teuton borrowed from the conquered provincial is a question still debated; the degree and the nature of Rome's influence on the new rulers varied in every province, indeed in different parts of the same province. The fact of the debt remains, suggesting a doubt whether in this case it was indeed the fittest who survived. The flaws in a social order which has collapsed under the stress of adverse fortunes are painfully apparent. It is natural to speak of the final overthrow as the judgment of heaven or the verdict of events. But it has still to be proved that war is an unfailing test of worth; we have banished the judicial combat from our law courts, and we should be rash in assuming that a process obviously absurd when applied to the disputes of individuals ought to determine the judgments of history on nationalities or empires.

The immediate and obvious causes which ruined the Western Empire were military and political - the shortcomings of a professional army and professional administrators. If asked whether these shortcomings were symptomatic of evils more generally diffused through other ranks and classes of society, we must go deeper in the analysis of facts. No a priori answer would be satisfactory.

The beginning and the end of the disaster were successful raids on Italy. Alaric and his Visigoths (401-410 A.D.) shattered the prestige and destroyed the efficiency of the government which ruled in the name of the feeble Honorius. The Ostrogoths under Theodoric destroyed the last simulacrum of an imperial power rooted in Italy (489-493 A.D.). After Theodoric had vanquished Odoacer, it was clear that the western provinces would not again acknowledge an Emperor acclaimed at Ravenna; although the chance remained that they might be reconquered and reorganised from Constantinople. This chance disappeared when the Lombards crossed the Alps (568 A.D.) and descended on the Po valley. From first to last Italy was the key to the West. And these successive shocks to imperial power in Italy were all due to one cause. All three of the invading hordes came from the Danube. The Roman bank of the great river was inadequately garrisoned, and a mistaken policy had colonised the Danubian provinces with Teutonic peoples, none the less dangerous for being the nominal allies (foederati) of the Empire. The Visigothic raids, which were in fact decisive, succeeded because the military defences of the Western Empire were already strained to breaking-point; and because the Roman armies were not only outnumbered, but also paralysed by the jealousies of rival statesmen, and divided by the mutinies of generals aspiring to the purple. The initial disasters were irreparable, because the whole machine of Roman officialdom came to a standstill when the guiding hand of Ravenna failed. Hitherto dependent on Italy, the other provinces were now like limbs amputated from the trunk. Here and there a local leader raised the standard of resistance to the barbarians. But a large proportion of the provincials made peace on the best terms they could obtain. Such are the essential facts.

Evidently the original error of the Romans was the undue extension of their power. This was recognised by no less a statesman than Augustus, the founder of the Empire; but even in his time it was too late to sound a retreat; he could only register a protest against further annexations. Embracing the whole of the Mediterranean littoral and a large part of the territories to the south, east, and north, the Empire was encumbered with three land frontiers of enormous length. Two of these, the European and the Asiatic, were perpetual sources of anxiety, and called for separate military establishments. That neither might be neglected in the interest of the other it was reasonable to put the imperial power in commission between two colleagues. Diocletian (284-305 A.D.) was the first to adopt this plan; from his time projects of partition were in the air and would have been more regularly carried out, had not experience shown that partitions led naturally to civil wars between rival Emperors. In 395, on the death of the great Theodosius, the hazardous expedient was given a last trial. His youthful sons, Arcadius and Honorius, were allowed to divide the Empire; but the line of partition was drawn with more regard to racial jealousies than military considerations. It extended from the middle Danube (near Belgrade) to a point near Durazzo on the Adriatic coast, and thence to the Gulf of Sidra. East of this line lay the sphere of Greek civilisation, the provinces which looked to Alexandria and Antioch and Constantinople as their natural capitals. West of it the prevailing language was Latin, and the higher classes of society modelled themselves upon the Italian aristocracy.