About100000 years ago, the northern hemisphere became dry and cold due to the great changes in the angle of the earth's rotation axis and the internal climate regulation mechanism of the earth. A large number of people who originally lived in temperate Siberia migrated to all parts of the world. Some of them migrated to America and some to the west, but most of them went south along the grassland at the eastern foot of the Caucasus mountains. Today, most Africans are Asians. In the process of migration, some ancient Germans established the Persian Empire, while others migrated eastward to Tianshan Basin and Indian Plain.
As we know, nomadic tribes often take a break during the migration process and then continue to migrate. In the Tang Dynasty, Xuanzang followed the migrating Germans to India. It is estimated that this is the last batch of Germans who left the Siberian Plateau, with a total number of no more than 600,000 (I estimate that the total number of survivors may exceed 654.38+10,000, but there must be a large number of deaths during the migration, and the death toll should be around 40%, so it is determined that the total number of these people is around 300,000, which is bound to be mixed with other ethnic groups following the migration). They are leading cattle and sheep in wagons with farm tools-the Germans are migrating.
Accurately speaking, today's Tajiks are mainly Germans, and they have merged with other ethnic groups. Among them, there will be others who migrated with the religion of ancient Persia and the Islam that came into being later. They abandoned their original religion and accepted a new one.
I only pay attention to prehistoric civilization for the time being, but I haven't had time to pay attention to some later things. I haven't got a clear idea about some traces of historical migration and integration before and after the Silk Road, so I can only give such a general answer for the time being.