How did tensions increase between the USA and Soviet Union from 1917 to the start of the Truman Doctrine?I need to know which key events cause...

The first cause of the tension was the actual creation of
the Soviet Union and the civil war that Russia went through during that creation.  As
the Soviet Union was being created, the United States government opposed the
Bolsheviks.  They condemned the Revolution and they sent a few troops to try to help
defeat the communists.  This showed that the US really did not like the idea of a
communist government and it helped make the USSR suspicious of the US.  After that, the
US did not recognize the existence of the Soviet Union for over a
decade.

The other major cause of tensions was the issue of
how to split up Eastern Europe (and to some extent Asia) at the end of WWII.  This
caused tension because the US thought the Soviets were overly expansionist and the
Soviets thought the US was trying to encircle and destroy them.