I recently had a friend attribute the collapse of the USSR (at least partially) to the falling energy prices of the 1980's and that got me thinking: Just how integrated was the Soviet Union with the global economy? How integrated were other regimes like Maoist China and post-war Vietnam? I know this is going to differ from country to country over time, but I had always pictured the USSR as a more or less closed system, something like massive autarky and now I am curious.
I can only comment on the Soviet Union during the NEP and Stalin periods. Hopefully it will be of use.
From 1921 onwards, ie after the disruption of the Civil War, the Soviet Union was never entirely disconnected from the world market and nor were there grand plans to do so. While the value of foreign trade dropped sharply from the pre-war high (and became a state monopoly), this fall was a function of the economic collapse, the loss of western territories and the internal restructuring of the agricultural market. Despite this, the Soviet government continued to see exports as a means to fund the import of Western technology and machine tools. (The use of economic concessions to attract economic investment was less attractive and petered out by the mid-1920s.) As the Soviet economy recovered then so too did the value of external trade: by 1927 the value of Soviet exports was about half that of 1913 (bearing in mind the caveats of changing borders and prices).
This balance of payments issue became even more acute during the Stalin years when exports and debts spiked during the FFYP to pay for the required technical expertise and imports (exports peaking at 90% of 1913 exports in 1930). Much of the pressure on the state to secure marketable grain came from the need to export higher volumes at lower prices. This obviously had a disastrous impact on the Soviet economy and exports crashed in the early 1930s as the years of hardship set in and world prices continued to weaken. During the industrialisation period it was a lack of ability, rather than an ideological preference for autarky, that limited foreign trade. Even then, the value of exports continued at around the NEP level (with higher volumes, given lower prices).
So that is a very brief summary of the contours of Soviet trade before 1940. The vast majority of Soviet exports were commodities: primarily grain and agricultural produce but also timber and rare materials. The idea was not autarky but to export these to finance the development of an industrial economy. I'd imagine that in later decades oil was seen similarly.
Sources: Davies and Carr's many volumes on the development Soviet remains superb but for a shorter introduction see Lewis' paper on Soviet foreign trade in The Economic Transformation of the Soviet Union
Soviet Union was dependent on the foreign grain, but only thing it managed to export was oil and other raw materials (and military equipment).
Here is nice piece by late Jegor Gaidar (sp?), found it via /r/Economics.