The contrast between Constantinople and the Cape, so finely drawn in these lines, marks the end of the age when land-communications and land-power were predominant over sea-power. The Roman Empire was, and could only be, a land-power. It is no accident that the British Commonwealth is, as the American Commonwealth is fast becoming, predominantly a sea-power. How was 'the greatest of all human responsibilities', arising from this new intercourse of races, met? Knowledge, alas, is as much the devil's heritage as the angels': it may be used for ill, as easily as for good. The first explorers, and the traders who followed them, were not idealists but rough adventurers. Breaking in, with the full tide of western knowledge and adaptability, to the quiet backwaters of primitive conservatism, they brought with them the worse rather than the better elements of the civilization, the control of environment, of which they were pioneers. To them Africa and the East represented storehouses of treasure, not societies of men; and they treated the helpless natives accordingly. England and Holland as well as the Latin monarchies treated the natives of Africa as chattels without rights and as instruments for their own ends, and revived slavery in a form and upon a scale more cruel than any practised by the ancients. The employment of slaves on her own soil has worked the permanent ruin of Portugal. The slave trade with America was an important source of English wealth, and the philosopher John Locke did not scruple to invest in it. There is no European race which can afford to remember its first contact with the subject peoples otherwise than with shame, and attempts to assess their relative degrees of guilt are as fruitless as they are invidious. The question of real importance is how far these various states were able to purge themselves of the poison, and rise to a higher realization of their duty towards their races whom they were called by the claims of their own superior civilization to protect. The fate of that civilization itself hung upon the issue.[56] The process by which the Western peoples have risen to a sense of their duty towards their weaker and more ignorant fellow citizens is indeed one of the chief stages in that progress of the common life of mankind with which we are concerned.