Dont forget that the Great King of Persia, Darius I Hystapes the Achaemenid also invaded Russia and was eventually defeated.
The Scythian strategy was to draw the Persians deep into Russia and force Darius over-extend his supply lines, exposing them to attack. Ironically is was only by the unexpectedly strong loyalty of his historically least trustworthy subjects, the Ionian Greeks, that Darius was able to escape the Ukrainian stepe with his life.
I think that history has shown that it is impossible to conquer a land as vast as Russia with out the help of local allies.