At the risk of sounding like a US apologist, I must respectfully add a rather large point that is missing from this discussion. I am in no way excusing US behavior in any way.

I am, of course, talking about the history of the Soviet Union, communism, and it's lasting legacy after the Soviet Union collapsed. The history of Tsarist Russia, while not essential, will bolster one's understand what I am talking about.

The Russian Revolution and Containment

To understand the Cold War, you must understand the birth history of the Soviet Union. For 60 years prior to the 1917 revolution there was a bitter class struggle between the landed elite and the recently freed surfs. This fertile ground is where The Communist Manifesto seed was planted The Russian Empire had a series of popular unrests throughout the late 19th century and the early 20th century, which culminated in the abdication of the Tsar, the withdrawal of Russia from World War I, and sparked the Russian Civil War.

The western Allies, who were still fighting the central powers when Russia withdrew from the eastern fronts, embarked on a series of seizures of Russian ports for supplies to prevent their capture by German forces and to prevent the spread of Bolshevism into other parts of Europe and America. Because the Western Europeans were still entangled in the western front, and aided by the first Red Scare, the US entered the Civil War on the side of the Whites to defeat the Bolsheveks and recreate the eastern front. Other powers at the time joined forces with the Americans, including the British Empire colonies, China, Canada, and Japan against the Reds for many of the same reasons. After World War I was concluded, the rest of the western powers joined forces against the Reds.

This Containment had a profound psychological effect on the Soviet leadership. Throughout the 1920s diplomatic contact outside the Comintern was virtually nonexistent.

Post-WWII

After the defeat of the Axis powers, the Soviet Union once again found itself competing diplomatically, economically, and ideologically with the west. Fears of a new wave of containment as well as competition for allies led to a wave of sponsored revolutions and annexations in Eastern Europe in what is now known as the Iron Curtain and later the Warsaw Pact. The Allies basically believed the Soviets were attempting another push to take all of Europe, resurrecting fears from the 1920s, and formed NATO as a counter to the Eastern Bloc. The former allies relationship quickly chilled. During the 1950s, the Soviets asserted their authority by violently put down popular revolts in Hungry, Poland, Czechoslovakia, and East Germany.

The biggest change was the advent of nuclear weapons by the United States and shortly after the USSR. Escalating fears and threats of nuclear strike by both sides led to a massive buildup in armament on both sides, justified as a response to a Bomber Gap, and later ICBM Missile Gap, perceived by both sides. Suddenly any aggressive military action could escalate up with nuclear strikes disturbingly quickly. The nuclear arms race continued until the MAD and deterrence became the prevailing military strategy for both sides.

Proxy War and Spheres of Influence

Because of the threat of nuclear war, neither side could engage each other directly. The NATO strategy was to contain the spread of Soviet influence around the world, while the Soviets maneuvered for influence as well as creating buffer states.

Korea became the first proxy battle outside Europe, with China and the Soviet Union supporting the communist north and the US and NATO supporting the democratic south. Vietnam, Congo, Greece, and Cuba saw direct conflict as part of this strategy. Combined with the collapse of the European colonial system, the shift in focus moved from Europe to the rest of the world. Various levels of support to communist movements expanded in the 1960s and 70s into the Americas (Peru, Cuba, Nicaragua), Africa (Somalia, Ethiopia, Congo, Angola), Middle East (Egypt, Syria, Yemen) and Asia (Afghanistan, Laos, Vietnam, Cambodia). This expansion of influence is partly explained because, as these countries entered into the UN, they were a source of sway between the two superpowers. Additionally, the Brezhnev Doctrine committed all pro-Soviet countries to supporting other communist countries against hostile capitalist takeover.

Post-Soviet World

After the dissolution of the USSR in 1991, NATO and the US found themselves without a rival. Alliances forged through the policy of containment were no longer necessary, and pro-Soviet governments found themselves without support. Popular revolutions cropped up across the globe, especially Eastern Europe, as both US and Soviet support of governments were pulled back after decades of meddling with ethnic tensions. The vacuum of power left by the Soviets made the US the only superpower, and the US continues to have a difficult time ratcheting down it's involvement. In many ways, the War On Terror mirrors the ideology and machinations of Cold War style Containment. The US isn't without some heart though, as it attempted to intervene against atrocities in Somalia, Kosovo/Bosnia/Serbia, and Libya. It doesn't excuse decades of negative influence, nor meddling in a post-Soviet world, but they are signs of a positive direction during a painful foreign policy realignment.

tl;dr

Soviets feared being “contained” by the west, engaged the US on influence in world events and countries, cracked down harshly on dissent within and without, those influenced by either side are still feeling the effects of the Cold War influence, and the US hasn't figured out how to act in a post-soviet world.

It's 2am and I can barely think anymore. I'm not a historian, but I did stay in a Holiday Inn Express. Smarter people than I, feel free to critique.

Sources: A shitload of Wikipedia.

• Cold War
• Soviet Union
• Russian Civil War
• Allied intervention in the Russian Civil War
• A whole bunch of others that I'm forgetting because I closed the browser window.