The power of the invasion lies in brute force and numbers. It is a case of a lower civilization temporarily overcoming a higher one—temporarily, because the rude virility which enables the invaders to maintain their own customs for a time succumbs eventually to the enervating influence of a civilization to which it is not trained. Civilization in the end proves itself more permanent than barbarism. This result is often furthered by the fact that the physical stock of the higher race is improved by the infusion of new blood from the very foreigners who are attacking it. This effect upon the physical stock may be very profound and lasting, as an invasion customarily involves large numbers of people. But while the invaders may succeed in checking the progress of civilization for a time, they seldom leave any permanent monuments of themselves, either material or institutional. They are not likely to affect the language, religion, or social customs of the invaded nation to an important degree. The mores are more enduring than the racial stock of the people who possess them.

There have been numerous instances of invasions in the history of Europe. In fact, the barbarian invasions are perhaps the most important single factor in the history of that continent during the Dark Ages. An excellent example is furnished by the Goths, particularly by the eastern division of that people. The original home of this people was in East Prussia, near the Baltic and the Vistula, where they were known in Roman days as traders in amber. There were two principal branches, the western or Visigoths, and the eastern or Ostrogoths. Their physical and mental characters were well marked and definite. In physique they were tall, blond, and athletic, in disposition brave and generous, patient under hardship, chaste and affectionate in their family relations. As to their habits of life before their migration, we have no very complete picture. In general, they seem to have been living on the pastoral-agricultural stage. They had no cities or villages, but lived in scattered dwellings upon farms, which they cultivated with the aid of slaves descended from captives. Much of the land was held in common, and upon it were pastured the vast herds of cattle which constituted their chief subsistence. The powers of government were centralized in a king, chosen by popular voice from certain great families. They had progressed far enough in learning to have an alphabet, but had not developed any written literature.

It is evident, then, that the Goths were a settled people, and while the ties which bound them to their home land were not very complex, and they were undoubtedly used to long warlike expeditions, yet there must have been some powerful motives to induce them to leave a land where they had become so well established. As to the exact nature of these motives, and the causes which lay back of them, there is no accurate record. It is not probable that they were driven out by the pressure of stronger neighbors. “Most likely it was simply the natural increase of their population, aided perhaps by the failure of their harvests or the outbreak of a pestilence, that made them sensible of the poverty of their country, and led them to cast longing eyes towards the richer and more genial lands farther to the south, of which they had heard, and which some of them may have visited.”[[6]] This explanation is admittedly largely based on guess. But it has every element of probability and marks the movement of the Goths as a perfectly typical example of a migration due to economic causes, natural overpopulation, augmented by temporary natural calamity, arousing motives of dissatisfaction through comparison with other seemingly more desirable regions.

Whatever the causes, the Goths determined to move. Uniting with the Gepids, Herules, and some other kindred peoples, they formed a great throng, which moved through what is now western Russia to the shores of the Black Sea and the Sea of Azov. Thence they journeyed westward to the north bank of the Danube. On the way they were joined by other groups of people, of Slavonic race. Their real history may be said to begin about 245 A.D., when they were living near the mouth of the Danube, under the rule of the Ostrogoths. For about twenty years they had been the allies of the Romans, who paid them money to defend their borders from the attacks of other would-be invaders. The Roman emperor, Philip the Arab, put an end to this payment, thereby arousing the anger of the Ostrogoths, who crossed the Danube and plundered the Roman provinces. This was the beginning of a long series of invasions extending down into Greece and Asia Minor. Many cities were plundered cruelly and brutally. Fortunately for civilization, however, the Goths had been converted to Christianity in the meantime, so that the army which finally entered and devastated Rome in the year 410 was not the utterly barbarous throng which had started on the journey from northern Europe. Their leader, Alaric, was himself a Christian and did what he could to restrain the natural passions of his followers. Yet in spite of all, the sack of Rome was a cruel and bloodthirsty affair.

It is characteristic of an invasion that over two centuries were consumed in the journey from the old home to Rome, so that no single individual of those who started on the undertaking lived to reach the final destination. For nearly a century and a half after the fall of Rome the Ostrogoths lived in or near Italy. Their fortunes in war fluctuated, and for a time, under Theodoric, they were the masters of the peninsula. Their kindred, the Visigoths, were in the meantime settled in Gaul and Spain. Finally, in the year 553, after repeated reverses, the Ostrogoths retired from Italy to the north, and as a people disappeared from history, leaving scarcely a trace behind. The Franks were never driven from Gaul, but eventually lost their native language and became absorbed in the people whom they had invaded. The Goths “have bequeathed to the world no treasures of literature, no masterpieces of art, no splendid buildings. They have left no conscious impress on the manners or the institutions of any modern European people.”[[7]] Even Gothic architecture has no historic connection with the people whose name it bears.

Other barbarian tribes invaded Europe at about the same time as the Goths, and during the succeeding centuries. One of the most powerful was the Huns, a people of rude culture but great virility, belonging probably to the Mongolic or Tatar stock, who appeared about the fourth century A.D. They were followed by other races from the same general region and belonging to the same great stock, the Avars who arrived about 555, and the Magyars who put in an appearance at the close of the ninth century. The most recent explanation of the migrations of these Asiatic tribes is that their habitat suffered a change of climate from one of those great cycles about which we are beginning to have some information, which resulted in drying up the region, and furnishing a much smaller amount of subsistence than the people had been accustomed to. This is overpopulation, and furnishes another case of that great economic cause.[[8]] Another powerful Asiatic invader was Timur or Tamerlane, who with his Tatar hordes devastated Asia Minor during the latter part of the fourteenth century.

A conquest is almost the reverse of an invasion. In this case the people of higher culture take the aggressive. It is an overflow of civilization, of manners, of organization, of government,—not to any great extent, of population. Conquest occurs when a well-developed state, full of vigor, sends its armies over the territory of less advanced peoples, imposing its political system upon them, and laying them under tribute, but not slaying the people or destroying their wealth any more than is necessary to secure subjection. It is an enterprise of the state, seeking its own glory and aggrandizement. The movement of population to the conquered territory may be insignificant, and in this, conquest differs from all the other forms of migratory movements. Consequently the effects on the racial stock of the conquered people may be very slight, and in most cases are. The effect on the mores, on the other hand, including the language, may be profound and lasting. Conquest differs from the other forms of migration also in the fact that the motives belong more nearly to the positive, or attractive, group than in any of the others. It is energy, ambition, etc., which lead to conquest rather than fear, cowardice, etc. Many of the individuals who change their residence under conquest are state officials, sent out in the pursuit of their duties to the sovereign, not because of any particular choice of their own.

It scarcely need be said that the great historical example of conquest is Rome. Her policy was to extend her dominion by making outlying tribes realize that it was to their advantage to acknowledge her sway and pay tribute. So long as they did this quietly and regularly, little else was required of them. As far as possible, the native governmental organization was continued, and simply grafted on to the great Roman stock, the native officials being made subordinates in the Roman organization. Roman traders came and went, carrying culture and civilization with them, and exerting a powerful influence on the mores of the provinces, but the permanent movement of people from the central state was comparatively slight. Alexander the Great was a spreader of conquest, though his early death destroyed whatever possibility there may have been of his establishing a permanent empire. The career of the British government in India has many of the characteristics of conquest. Native rajahs are, to a great extent, utilized as officials of the British government, and there is no large migration of people from England to India, save those connected in some way with the government service, or persons engaged in commercial pursuits, who maintain their permanent home in England. But the influence on the mores of the native inhabitants is great.

The third form of migratory movement, which has a particularly close connection with immigration, is colonization. This occurs when a well-established, progressive, and physically vigorous state sends out bodies of citizens, officially as a rule, to settle in certain specified localities. The regions chosen are newly discovered or thinly settled countries, where the native inhabitants are so few, or are on such an inferior stage of culture that they offer but slight resistance to the entrance of the colonists. For while the two previous forms of migration have been warlike, colonization is essentially a peaceful movement. The rivalry for certain favored localities may involve the colonizing power in war with other civilized nations who desire the same thing, but as far as the seizure of the colony itself is concerned, it requires slight military exertion. Colonization, like conquest, is a state enterprise, conducted for the benefit of the state, but differs from it in that its motive is rather the commercial advancement of the state than its military or political aggrandizement. Colonization has often been resorted to, also, when a state has believed itself to be overpopulated, and has aimed directly at improving the condition of its citizens, both those who go and those who are left,—something that is scarcely dreamed of under conquest. Several classifications of colonies have been made. The most satisfactory is that adopted by Professor A. G. Keller, which makes a twofold division into farm and plantation colonies.[[9]] These differ from each other so much in their essential characteristics that it will be well to examine them separately, before making any further generalizations regarding colonies as a whole.

This classification is based on the typical form of the industrial organization in the colony. As colonies are always new and undeveloped regions, the fundamental industry is always of an extractive nature, almost universally agriculture in some form, though it may be mining or fishing. Practically all important colonies in the history of the movement, however, have been agricultural, so that the above division serves every purpose. In the first place, it must be noted that practically all colonizing nations have been situated in the north temperate zone, and primarily in Europe. Outside of this continent, Phœnicia and China are the sole important representatives. These, with Greece and Rome, made up the colonizing powers of the ancient world. As far as modern colonizing nations are concerned, the question is limited to the countries of Europe.