I read the first half of Young Stalin, by Simon Sebag Montefiore, and the origins of Stalin's injury are unclear. It is most commonly believed to come from a carriage accident.

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Voice or no voice, the people can always be brought to the bidding of their leaders. All you have to do is tell them that they are in danger of being attacked, and denounce the pacifists for lack of patriotism and exposing the country to danger.
--Hermann Goering