The Berlin sector border is sealed

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Overnight on 12–13 August 1961, East German forces closed the sector boundary in Berlin with barbed wire and began building a permanent barrier, ending the last open crossing point between the two systems in Europe. The immediate driver was emigration: the loss of population through Berlin had reached a rate the East German state could not sustain. The western powers protested and did not intervene, having concluded that their essential interests were access to and the freedom of West Berlin rather than free movement across the city, and those were not being challenged.

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