Answer:
D
Step-by-step explanation:
A) The Soviet Union used to control all of Ukraine and Putin wants that former territory. The Ukraine people were also heavily suppressed and treated horribly in the former Soviet Union.
B) NATO was created at the start of the cold war between the Soviet Union and United States. It was essentially made as an alliance against communism and the Soviet Union. In present day, Putin believes that NATO is over stepping its bounds into what Putin believes to be his rightful sphere of influence.
C) The Iron Curtain was the Soviet Union's former territories, which consisted of mostly countries surrounding present day Russia. This includes Ukraine. The Iron Curtain was essentially the Soviet Union's version of NATO, where the Iron Curtain countries would protect the Russian motherland from invasion.
D) In conclusion, all of these answers contribute to the historical context of the current situation in Ukraine and Eastern Europe.