They're indigenous to a part of modern day Russia. Based on their genetic composition and linguistics (as well as their own distribution) they likely migrated

They're indigenous to a part of modern day Russia. Based on their genetic composition and linguistics (as well as their own distribution) they likely migrated from central Asia northwards, to Siberia, northern Russia, Finland, northern Sweden, etc... The other major Uralic group (Magyars/Hungarians) went south, joined with Khazar groups, and eventually spread to modern day Hungary. No archaeologist or historian doubts that Slavs are indigenous to the territory that is modern western Russia/Belarus/Ukraine...