Write a precis of following paragraph in about 102 words. Several times in the history of the world particular countries and cities or even small groups of people have attained a high degree of civilization. Yet none of these civilizations, important they were, have lasted and one of the reasons why they did not least was that they were confined to a very few people. They were like little oasis of civilization on deserts of barbarism. Now it is no good being civilized if everybody round about you is barbarous, or rather it is some good but it is very risky. For the barbarians are always liable to break in on you, and with their greater numbers and rude vigor scatter your civilization to the winds. Over and over again in history comparatively civilized people dwelling in cities have been conquered in this way by barbarians coming down from the hills and burning and killing and destroying whatever they found in the plains. in the thirteenth century most of Europe was overrun in this way by the Mangols from Central Asia, and such civilization too for beyond its neighbors has always been liable to be set upon and pulled back by the others, just as, if you build a high tower without proper support, it is always liable to fall down to the level of the lower buildings round about it. Now one of the noticeable things about modern civilization, which is also one of the reasons why it is likely to outlast the others, is that is more or less free from this particular danger. And it is free from it, because it is far less local and far more widespread than the other, so widespread indeed that it already covers a large part of the earth.