You need to go farther back in time than the Soviet invasion of Afghanistan. Start with the end of World War II.
These sites should help you.
http://en.wikipedia.org/wiki/Cold_War
http://www.historylearningsite.co.uk/coldwar.htm
i need ti write a paper on why the soviet union is to blame for the cold war. could an example i cit be when the soviet union invaded afghanistan?
3 answers
why do i need to do that? I have to focus on events of the 1970s and 1980s
Blame is usually attached to the beginning of a conflict. However, the articles above detail the Cold War in the 70s and 80s so you should find lots of information there.