I can and its been pretty easy. Very easy difference between Polish/Russian/Slavic folk. Slavic is the base for Russian folk. Slavic Kingdom reached in the End till Russia. where later on the declare them self as a Kingdrom. That why also the Language of Slavic and russian in based on the same old slavic language.
By the Way Russian has an old Slavic, Nordic Influence, thats why you also find old Viking town in Russia. Thats why there also so much Finn/Russian Russian/Finn its a part of the old History.
But that comes maybe from my work cause i work Daily with all part of europen People.