By having specific politics imposed on them.
I do not think that was the only variety of screwage inflicted on the Soviet bloc countries by the USSR.
(And I bet imposing a particular political system on a country tends to make it less prosperous than it would have been had it adopted that political system of its own accord -- because the people who have to make it work will resent it, be less motivated to make it work well, etc. So even if that were all the USSR did, I'd still expect economic damage independent of the (de)merits of the particular system they imposed.)
If by "socialism" you mean [...]
Actually I mean something more like "that which Western social democracies have more of than Western free-market capitalist countries, and avowed communist countries have more of again". Or like the big bag of ideologies you'll find on Wikipedia.
And I bet imposing a particular political system on a country tends to make it less prosperous than it would have been had it adopted that political system of its own accord
Counter-example: post-WW2 Japan (and, arguably, Western Germany as well).
Generally speaking, I'd say that "people who have to make it work will resent it" is too crude of an approach. Some people will, but some people will see it as an excellent opportunity to advance. In the case of the Soviet Union itself it's unclear whether you can say that the political system was "imposed" -- it's not like the population had a free choice...
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