Question

when hungary opened its borders, it created a \hole\ in the government iron curtain berlin wall revolution

Explanation:

The Iron Curtain was a metaphorical division between Western Europe and the Eastern Bloc during the Cold War. When Hungary opened its borders, it provided an escape route for East Germans to the West, thus creating a "hole" in the Iron Curtain. The Berlin Wall was a physical barrier in Berlin, Germany. Government and revolution are not relevant in this context.

Answer:

Iron Curtain