Most societies (ancient and modern) naturally gravitate towards organising themselves in various strata. Higher, lower, richer, poorer, important, unimportant, better, worse. The various peoples scattered across the globe can be so different - and yet exhibit so many common traits. Of course there are differences in the ways in which those shared traits are manifested - they have been defined by local culture / history / etc - but the common traits remain. 'Class' is just a word, particularly and popularly attributed to Britain, but you'll discover different manifestations of something similar almost everywhere you care to look.