Major/Minor in World Literature

The actual practice of the study of world literature has almost invariably limited itself to studying the literatures of a very few major literatures. In fact, for the longest time world literature seemed to consist of only a few European literatures. Of late, this practice has come to be challenged from the perspective of other, non-European or non-Western, major literatures. But what in fact makes a literature qualify as major, or, inversely, as minor? What factors are involved: quantitative, qualitative, or yet other?