K constantly aiming to avoid closing border, but changed his mind over large numbers of citizens migrating. 10,000 in the first half of 1961. Many skilled workers and so essential to economic growth.
Walter Ulbricht, East Germany chancellor, persuaded K to act. On 13 Aug 1961, work began to physically seal off West Berlin.
At first, wire fences, then a concrete wall with deep perimeter defences. There were 4 recognised crossing points. US and Soviet tanks faced each other at Checkpoint Charlie.
Arguably - West Berlin's success is what led to enhances conflict with the East, who were now determined to prove themselves just as prosperous as the FDR had become. Easy travel from one into the other only highlighted the disparity between the two states, and allowed all to view the stark difference for themselves.
Over 500,000 over the previous two years, by the end of 1956 showed that well over a million more had departed from the East.
K's ultimatum initially established to allow the GDR time to better itself, however time was only lost, with more and more moving - the population of the GDR had declined since 1949, from 19 to 17 mill.
Major crisis for Communism - Mikoyan warns in July 1961 that this could be the end.
Ulbricht had plans in place since 1952 at least to prevent travel continuing from East to West Berlin, via building a wall around the West. Had been resisted by Soviet leaders. K thought that a better method of dealing with the unrest would be to created better living conditions in the East.
Janos Kadar, Hungarian leader, predicted fate of the Berlin Wall in 1961, claiming it was more dangerous for the communist ideology than for the actual circumstances that it brought about within the city.
K even admitted that the wall was a 'hateful thing', but claimed helplessness and no other resort.
The wall was erected on the night of Aug 12-13, 1961. Saw the stabilisation of East Berlin's economy - kept everyone in. Provided a resolution that was not literal war, or possible use of nukes.
When Kennedy visited in June 1963, noted that the US never had to build a wall to keep everyone in.