How the wall came to be

http://www.slate.com/id/2234900/pagenum/all/#p2

Khrushchev had never intended to occupy West Berlin, and the wall represented the act of locking in eastern Germany from pouring out of the country to the west. It was a gateway to the west, a way of escaping the communist regime.
"Khrushchev's threat stemmed from desperation. Over the previous decade, West Berlin had grown free and prosperous while East Berlin had stagnated under the Soviet boot. Easterners were emigrating to the West in droves, using West Berlin as their transit point. By the fall of 1958, East Germany had lost 2 million people, with continued losses of 10,000 per month, including some of its best-educated youth. Khrushchev needed to stop the hemorrhage."