The correct answer is: "The Berlin Wall is built".
The division of Germany took place during the Postdam Conference, celebrated in 1945 right after the end of WWII.
The Korean War started in 1950, after the country was splitted in two halves and the North attacked the South, and lasted until 1953
The Warsaw Pact was signed by the URSS and its satellite Soviet republics from Eastern Europe in the aftermath of WWII in 1955, in order to create a joint defense strategy against the NATO.
The Berlin Wall was built in 1961. The German Democratic Republic, as a satellite state of the URSS, explained that it was built to prevent the influence of harmful capitalism in its territories, although the basic reason was to stop the population flows that were moving from East Germany to West Germany.
