Short answers, pulled from the story.
The new Bolshevik regime instituted passport controls in the first month after the Russian Revolution of 1917. This move forbade the exit of belligerent nationals from the country to prevent opposition and inflate opposition armies.
By 1945, the additional annexed countries totaled approximately 465,000 square kilometers. These included Eastern Poland, Latvia, Estonia, Lithuania, and parts of Romania under direct Soviet control.
Before 1961, over 3.5 million East Germans emigrated to West Germany through Berlin. This number represented approximately 20% of the entire East German population at that time.
Two days later police and army engineers began constructing a more permanent concrete wall on the 15th of August 1961. The completion closed the biggest loophole in the Iron Curtain during a decade of divided capital.
In August 1989, Hungary removed its physical border restrictions with Austria. The next month more than 13,000 East German tourists escaped to Austria through this new opening.