The social distance between members of different castes precludes intimacy, but this is altogether due to the simple objective fact that they belong to different organizations. The social distance between social classes has to do with exclusiveness based on the status and the corresponding learned responses of the persons concerned. Social classes divide homogeneous populations into layers of prestige and esteem, and the members of each layer are able to circulate freely with it.
Social distance, then is any social barrier between persons or groups. The kinds of social barriers may be described as horizontal, vertical, or mixed. A perfect example of a vertical barrier (dividing horizontal groups) is that which separates a British aristocrat from a Hindu prince. It reduces their relationship, typically, to one of formal recognition. The same is true of two Fifth Avenue merchants, one Japanese and one French. Their pride, each respectively, is not one of class, based on differences in status (it is presumed for the sake of the example); it not a caste barrier, because neither the British man nor either of the two merchants is a member of any caste organization; the barrier is racial and cultural. Nationalities, in general, resemble castes in one respect -- they are usually distributed on a horizontal scale. They live alongside, but apart.
The United States today experiences the heterogeneity of mixed kinds of social distance. There are French-Canadians, Mexicans, and a few religious sects (the Mormons, e.g.) which represent cultural, almost caste-like, differences. Orientals and blacks create cultural and racial barriers. Some white groups, with their strict codes and careful supervision of degrees of exclusiveness -- over against the disorganized and unorganized blacks generally -- maintain the caste type of social distance. The same is true of all religious groups that set themselves apart by wearing distinctive clothes (Amish, Mennonites, Orthodox Jews, etc.).
Exclusiveness based on status (social class) is a part of all civilized life, but the lines are not always formally drawn. Many of the activities engaged in by Americans, for instance, especially in war time, throw the members of the different social classes together often and in many ways. But social class feeling is ever present. Classes are almost universal; caste organizations are rare phenomena outside of India and Africa.