@Imperious:
Except for Germany in ww1
Incorrect, Russia was not conquered (in fact Germany conquered less of them in WW1 than in WW2). Just Lenin did a pact with Germany (Brest-Litovsk peace if I remember well) because he had to fight with zarists while kaiser accepted because he has too much to do against UK and France. As much you can say a minor victory for Germany since Russia lost Poland and also Baltic States, never a conquest
The powers than were more close to conquest Russia were Mongols and France. But Russia was not a nation at XIIIth century (just a bunch of small powers as Moscovy, Kiev and Novgorod) and Napoleon had to retreat from Moscow and finally lost the war
It’s higly difficult any power could conquest the full USSR. As much, conquer so much that russians would want coup Stalin. But even then you would change Stalin for someone that easily could be undemocratic anyway (Putin is not Lincoln, you know). Few profit for such high price