An ideological division between western and eastern Europe.
The Iron Curtain separated Eastern Europe (which is under the USSR control), which contained Eastern Germany, Poland, etc, in which these places were placed under a Communist government.
On the other hand, Western Berlin (As Berlin was also split), and the three western nations parts (later placed together to become Western Germany), was given a democratic-like government instead, and, with western aid, was able to grow economically and was able to be repaired quickly.
Because condition inside the West was better, Eastern Germans quickly moved west-ward in search for better conditions, leading to the USSR building the Iron Curtain to keep East Germans from escaping, which led to the symbol of the division between the Communist nations and the Democratic.
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Answer: An ideological division between western and eastern Europe.
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