Invading Russia

Three great militaries, that of Charles XII's Sweden, the Grande Armee, and the Wehrmacht have all invaded Russia and failed. 

What, in your opinion caused their defeat, and how would you invade Russia?

In my opinion, it has always been the logistical hardships imposed by the Russian winter and spring coupled with the extreme vastness of the country, nothing too novel.  I think the mistake by all three of the invaders was trying to take Russia all at once, they advanced too deep into Russia while inadequately prepared and then found himself fighting across a massive country without enough logistical support.  Thus, I would say that one cannot overtake Russia in one fell swoop, so I wouldn't even try.

Here's my plan to invade Russia from the traditional starting point of Eastern Europe:

Phase I:

First, I would send a minimum of 27 divisions to take Moscow and thus cut Russia in two (few railways to the east of Moscow run north to south), my divisions in the Ukraine and the Baltic would be sent on diversionary attacks and then told to settle down and defend after they've penetrated perhaps 60 or so km past the frontier.  After taking Moscow, a buffer zone of about 100 km would be created around the city, the frontlines would be fortified, and supply lines would be expanded and winter stockpiles created.  After this, I would settle down and defend during the winter and muddy spring, allowing the Russians to launch offensives I would destroy.  Throughout the winter, air attacks would be imperative to work to destroy russian industry and disrupt transportation

Phase II:

Once the spring mud has gone, I would launch an offensive with the aim of driving toward Astrakhan and Caucas Mountains.  Then, I would halt again, defend throughout the winter, and expand supply lines in the south.

Phase III

This phase would be much like the earlier two phases except now the target is the Volga river valley and Northern Russia.  This phase would involve an attack north from Volgagrad and one east from Moscow converging on Kazan.  St. Petersburg would also be taken.

Phase IV:

This phase might be able to be launched before winter, for at this time the Russians are probably on the brink of total collapse.  This phase would simply be the capture of the remaining major population centers in Russia and perhaps an advance into western Siberia if it is needed.

I think that this slow and methodical conquest would eliminate most of the problems that have defeated the massive campaigns that have aimed at defeating Russia on an impossible timetable.

Nice strategy to invade Russia indeed. But it seems you forgot to watch your back. How do you due with the revolts in the occupied regions and protecting your supply line ?

You'd need a very very large army to keep advancing and defending the occupied area. So you'd also need a massive economy too.

A country could spend anything it has to defend itself, but it's not sufficient for a country to spend so much on an invasion. 

Secret Police baby!

Actually Britain occupied India for 2 centuries despite only having less than 2-3% the population of India.

Have you ever heard of divide and rule. Russian's don't exactly need an excuse to start fighting with one another. Some large quantities of arms given to the right people and they'll conquer themselves.