How could I structure an essay on the causes of the Cold War?

You want to avoid a chronological structure - thematic is best. Here is a suggestion of 3 themes:

1. Pre-existing tensions between the US and USSR before the outbreak of the Cold War. (Ideological differences, tensions during WW2 and the development of mutual suspicion)

2. US Provocations (Use of the atomic bomb, policy of containment, the Long Telegram and Marshall Plan)