Tensions between the U.S., Britain, and the Soviet Union began as early as 1943 when their three leaders met in Tehran to coordinate strategy over the ruling of Poland. They continued to escalate and came to a head when FDR died and Truman took over, taking a hard stance against Stalin.
During the Cold War itself, most historians and politicians agreed that it was caused by the Soviets and their evil dictator Stalin attempting to dominate the world with his Communist ideology. America reluctantly joined to save the world from a totalitarian regime.
After the Vietnam war in the 1960s, disillusionment was high and historical revisionists began to claim that although Stalin was a tyrant, he wasn't interested in world domination but merely in preserving the Soviet Union. He wanted to use Poland for security purposes and America misinterpreted that as a desire for conquest. Americans were to blame for the start of the Cold War as they aggressively tried to contain the Soviet influence, intimidate them, and actively pursue American economic interests in other parts of the globe.
A third and more recent interpretation, a "post-revisionist synthesis," incorporates the idea that America played a part with its aggressive and intimidating behaviors, but that Stalin was also a powerful and malevolent dictator who was partly responsible.