What were some of the defenses that made it almost impossible
to escape Eas
Berlin?

Between 1945 and 1988, around 4 million East Germans migrated to the West. 3.454 million of them left between 1945 and the construction of the Berlin Wall in 1961. The great majority simply walked across the border or, after 1952, exited through West Berlin. After the border was fortified and the Berlin Wall was constructed, the number of illegal border crossings fell drastically. The numbers fell further as the border defenses were improved over the subsequent decades. In 1961, 8,507 people fled across the border, most of them through West Berlin. The construction of the Berlin Wall that year reduced the number of escapees by 75% to around 2,300 per annum for the rest of the decade. The Wall changed Berlin from being one of the easiest places to cross the border, from the East, to be one of the most difficult. The number of escapees fell further to 868 per annum during the 1970s and to only 334 per annum between 1980 and 1988. However, escapees were never more than a small minority of the total number of emigrants from East Germany. Far more people left the country after being granted official permits, by fleeing through third countries or by being ransomed to the West German government. During the 1980s, only about 1% of those who left East Germany did so by escaping across the border.

Explanation:

they thoght they were going to nuke each other