Communisme in the soviet union

Consider the Fall of Communism in the Soviet Union. Based on your research, what do you feel was the main cause for its collapse? Was it due, for example,  to a lack of a consumer economy, poor leadership, or U.S. military competition? Be sure to backup your ideas with facts from our class and your own research. 
You should use the following web site as a resource. You will find on this site links to primary sources (sources written at the time), along with essays on the various countries that confronted communist rule head-on in the fall of 1989. How do these documents help to explain the fall of communism? This does not have to be your only source, but you are required to use and site the documents available here:     Be sure to include footnotes in your essays in CMS format.