If you want the Red revolution strangled in its crib the best way is to get rid of Trotsky. Say he is either killed or is unable to get to Russia. He was the one to reorganize the Red Guard in the Red Army and made it into an effective fighting force. Say without him the Bolsheviks are still able to seize power but are never able to put down White opposition once they start to get military aid from the West.
Say the communists have enough strength to hold onto Moscow until June of 1920 before they are overthrown and most of them killed. Prior to this you have the Czar and family being executed. There is going to be at least one claimant to the throne if not several. By this point World war One is over and whatever treaty the Germans imposed is voided. The British and French want a single stable Russia either under a constitutional monarchy or as a republic. However while they will send economic support and small expeditionary forces invading with huge armies and fighting a long drawn out war to unify the country is out of the question.
In reality Finland, Poland, Lithuanian, Latvia, and Estonia all managed to break away. Given even greater instability add to this a free Armenian state, the Ukraine, and the Crimea. In the Far East the Japanese could try and set up a puppet state using a pretender to the Czarist throne. The model they used in Manchukuo. The US and general world opinion would be opposed to this, but the British might support it if they remain Japanese allies. Faced with no serious military opposition and only diplomatic protests the Japanese would definitely go forward with establishing control over eastern Siberia.
What would be left after these defections might well be carved up among a number of generals. Each one too weak to conquer the others and willing to rule over his own country.
Entering the 1930's this situation would be heaven sent for the Japanese and Germans. For Japan Manchuria can be safely conquered as can be the 'Northern Resource Area.'
For Hitler the situation is literally perfect. To the east he has perhaps a dozen independent and weak states that do not trust each other. Not only will Germany be significantly stronger than any likely combination of them he can play them off against each other’s. Making alliances with certain states and gaining their support in exchange for territorial concessions from the victim. Just as he got Polish and Hungarian help with destroying the Czechs.
Hitler could ALSO use the excuse of coming to the aid of a threatened ally to help justify his aggressions. Faced with this situation Hitler would almost certainly be able to conquer or reduce to puppet status everything from Arcangel to the Black Sea.