Napoleon himself gave that answer.
It was not russia that defeated him. It was not England. He was defeated in his own words, by the Spanish ulcer. There is a book on that issue.
As far as I know, many of the soldiers of the Grand Armé sent to Russia, weren't even French. Many of them came from allied nations.
Unlike in the campaigns in Spain (which he conquered, but never dominated) and Portugal, (which he was never able to conquer at all), most of the soldiers were in fact french, because of the proximity.
No other place in Europe was so devastated as the Iberian Peninsula.
The Russian campaign, took some months and was a defeat. The Iberian peninsula took five years. There were victories and defeats, but no definitive victories, and no definitive defeats. When the British stepped in, and the allied armies started their advances, it was the begining of the end. Napoleon was defeated by the same thing that defeated Hitler. A war in two fronts.
Regards