The divisions between all these groups are approximate and their boundaries are not always clear. The Mizrahim for example, are a heterogeneous collection of North African, Central Asian, Caucasian, and Middle Eastern Jewish communities that are no closer related to each other than they are to any of the earlier mentioned Jewish groups. In modern usage, however, the Mizrahim are sometimes termed Sephardi due to similar styles of liturgy, despite independent development from Sephardim proper. Thus, among Mizrahim there are Egyptian Jews, Iraqi Jews, Lebanese Jews, Kurdish Jews, Libyan Jews, Syrian Jews, Bukharian Jews, Mountain Jews, Georgian Jews, Iranian Jews and various others. The Teimanim from Yemen are sometimes included, although their style of liturgy is unique and they differ in respect to the admixture found among them to that found in Mizrahim. In addition, there is a differentiation made between Sephardi migrants who established themselves in the Middle East and North Africa after the expulsion of the Jews from Spain and Portugal in the 1490s and the pre-existing Jewish communities in those regions.
Why are Mizrahim sometimes termed Sephardi in historical usage?