The announcement of the truman doctrine, the berlin airlift, and the formation of the north atlantic treaty organization were actions taken by the united states to prevent the

To prevent the expansion of communism into Western Europe.

Explanation:

The US Government under the leadership of President Truman had started taking steps to terminate the possibilities of a probable third world war with the view of 'saving the world' from its dreadful consequences. In order to do that, the US had to take certain steps to cease the expansion of communism in western Europe being attempted by Soviet Russia directly or by sponsoring other likeminded neighboring nations to do it.