Social causes: I think that the Cold War was caused a lot by fear. People were afraid of the spread of Communism because they basically tweaked out and yelled "Conspiracy!". They thought everyone who was Communist was anti-Democracy and anti-United States. Coming off of two World Wars, this fear was at least partly founded in logic. In the past it had seemed like countries of similar ideologies were more likey to become allies. This fear led to conflicts and interference in situations taht probably otherwise would not have merited very much attention.
Economic: Economics were definitely a contributor to the Cold War because economics is primarily what defined a country as Democratic or Communist. Impoverished countries mostly became communist, as ideas of equality appealed to the general population. Democratic countries were usually those for which the free trade and capitalist systems were working and needed little interference from a Communist dictator.
Political: In my opinion, political causes were the most significant of the causes of the Cold War. Communist countries set up the Warsaw Pact to unite Communist powers and defend themselves, and opposingly, the Democratic powers set up NATO. As seen previously in World War 1 and 2, establishing alliances served to increase paranoia and tension. These alliances also led to more competition over the undecided countries in Asia and South America. Because of the competitition between the two factions, political leaders became more and more dedicated to besting each other in all areas. The invention of the atomic bomb at the end of World War 2, the Space Race, these things are examples of how dedicated Stalin and Truman, as well as consecutive U.S. presidents were, to topping each other.
I don't think the blame can be assigned to either the United States or the Soviet Union exclusively. In certain instances, such as the Bay of Pigs, I think the United States seems like a bit more of an antagonist. However, Stalin did point missiles at us. So that wasn't cool either. Both countries just got a little too carried away in that trite old "world domination" bit and let their paranoia get the best of them.
