About 1980, at the height of the Cold War, I came to the conclusion that there would never be  war between the Soviets and America.  The second casualty in war is always the food supply, and the Soviets could not produce enough food to feed themselves in peace time, much less in war time.  Throughout the Cold War, the Soviets imported massive amounts of food, primarily from the USA. 

 

Before 1918, Russia did export grain as noted, but you will find that exports ended abruptly when the Marxists took over and Lenin shot and starved millions of poor Kulak farmers.  The Soviets imported food almost exactly coincident with the years of the Soviet state; The Soviets began importing food immediately after 1918 and Russia began exporting food again immediately after 1991. 

A critical reason why the Soviet Communists didn't maintain or improve the kinds of communications systems (trains, all-weather roads, river and canal routes) which enable a division-of-labor society to function as a market economy isn't just that socialists hate the voluntary exchange of goods and services in the marketplace (though that's certainly true), but that the Evil Empire was never anything but an "invader" which had conquered and was occupying the people of Russia and the other Soviet socialist "republics."

 

Robust routes of communication enable conquered peoples to coordinate resistance and even uprisings.  True, the Evil Empire could use those roads, railways, and rivers to shift armed goons hither and thither, but the problem for the Soviet Communists was always that they were a minority in a sea of Russians and other ethnic groups who would have happily slaughtered the commissars the moment they thought they could get away with it.  

 

 Take note of the passport system in the old Soviet Empire, which were required of the populace if any of them wanted to move around in their own country.

 

The Communists lived in terror of the proletariat getting around to coordinate with each other.  Commerce would facilitate that, and therefore both commerce and travel had to be impaired as a matter of state security. 

Very good points made here, communications being key bad news travels fast as the saying goes. The modern analogue is the PRC's system of internal and external firewalls, giving the CCP free reign to shut down 'negative' vibes as they see fit - for a nation that has boastfully installed a network of maglev trains to have willingly suppressed similar innovations in interconnectivity demonstrates what they are really scared of. 

 

Most western governments seem to be edging gradually towards a "regulated" communications space, for any power, authoritarian or otherwise, the ability to monitor and sanitise at will is extremely attractive - the internet's original "unregulated" origin will eventually be looked back on with the same sort of bewilderment that we now have for the pre-modern era of unregulated narcotics. The PRC is gradually and painstakingly edging its way towards greater respect for individual rights of expression, what worries me is that in almost all western nations the exact opposite is happening, except in our cases it is via subtle chicanery and diversion. 

 

R 

Historically it has been the other way around. Roads and railroads were built principally as a way to rapidly move troops, and the improvements in trade were just a fortuitous secondary benefit. Notable examples of this include the Romans, British Empire, the US starting in the Civil War, and the Inca’s. I suspect that the lack of roads to much of the Soviet Union may have been a major contributor to its collapse, as effectively remote regions (i.e. without addiquate transport links) just quietly rebelled and ceased to send their taxes to Moscow. Without roads this quiet rebellions would have been logistically impossible to suppress, especially when there was a distinct possibility that they would become active rebellions if the suppression efforts failed because of insufficient troop strength

The passport system is the way you restrict to movement of individuals, not poor roads. But the critical issue is not the movement of people, but of ideas, and that is a battle that totalitarian regimes are losing badly.