Discuss the origins of the Cold War and the sources of growing tensions between the US and the Soviet Union at the close of World War 2?

From the most fundamental of positions, neither the United
States or the Soviet Union really trusted one another.  Their alliance in World War II
was out of convenience.  Both saw Hitler as a threat and both needed the other the
negate it.  The Soviet Union signed a nonaggression pact with the Nazis and only when
Hitler invaded Russia did the Soviet Union ally itself with the United States.  The
mutual need to eliminate Hitler was an excellent source of cohesion.  When the threat
was ultimately eliminated, old tensions resurfaced.  There was considerable mistrust
about what a post- Hitler Europe would look like.  Stalin did not want to have another
attempted invasion of Russia, so his desire to create a series of buffers between it and
the rest of Europe was seen as expansionist by the West.  The threat and use of nuclear
weapons enhanced the fundamental mistrust between both nations.  These tensions which
were exacerbated by the peace conferences following the Nazi defeat ended up forming the
basis of the Cold War that followed World War II.