What was the most important cause of the Cold War?

When writing an essay where you have to say which is the main cause of the CW, it doesn't really matter which you choose, as long as you can explain clearly and confidently why you think that cause is the most important and you are consistent throughout the essay.

The main causes to choose from are:

- a history of mistrust between the USA and USSR

- their opposing ideological views

- WWII - USSR felt abandonded. Atomic bomb techonology created by USA not shared with USSR

- Soviet take over in Eastern Europe

- Truman Doctrine.  Marshall Plan

- Divison of Germany. Berlin Blockade.

It also depends what the time limits of the question are, and when you decide that the Cold War properly began, as this is not a fixed date. It is important that once you have chosen you main cause, that you try to demonstrate how this cause led to or influenced other important causes.