Western leaders breathed a secret sigh of relief on August 13, 1961, when a midnight action by the East German army sealed off the sectoral lines in Berlin and began the construction of a barrier all the way around West Berlin, ostensibly to foil an imminent Western invasion. Because the West did not intervene, this sudden move effectively resolved the conflicting claims to the entire city: the West implicitly accepted division and the East surrendered its claim to West Berlin.
