First of all it must be observed that the bulk of the accumulation has been accomplished by a relatively small number of individuals. If this concentration of wealth were peculiar to the United States it might be attributed to the fact that this country has undergone exceptionally rapid expansion, during which the opportunities for accumulation were both unusual and irregularly distributed. But the explanation seems to lie deeper, for the same condition is to be found in all advanced industrial nations. The opinion may be ventured that it is characteristic of such industrial arrangements as have prevailed in the United States, that the tendency towards diffusion of the results of advances in production (obscured, besides, by the growth of population) should lag seriously behind the tendency towards concentration.[11] The condition of inequality of wealth, heretofore a condition of the process of capital accumulation, is one of the chief causes of the embitterment of industrial relations. Firstly, it is one of the factors which tend to the creation of separate group interests. A high degree of inequality of accumulated wealth leads to a concentration of the control of the larger industrial enterprises within the hands of a small section of the community. The interest in high returns from accumulated wealth appears to be a group interest. And, indeed, if the lag of diffusion behind concentration passes a certain point it is in reality a group interest--in the sense of being opposed to the general interest. Secondly, great inequality of wealth leads to the growth of institutions incompatible with the purposes of a democracy. These are a cause of economic antagonism, which has its reflection in industrial relations. Thirdly, it has evil psychological effects. In a country bred upon the general ideas of democracy, not even political equality and a wide distribution of economic necessities and comforts will suffice to produce general contentment, if a top stratum of the community is possessed of the social advantages of vast wealth. Few are satisfied with their lot as long as they see others, often through no qualities of their own, more satisfactorily endowed with worldly goods. Lastly, although great inequality of wealth makes possible a high level of production, it also makes great waste possible.