It is difficult to pinpoint a 'cause' for a war. This is because there is no agreed-upon rule on how far back in history you are to go when you look for a cause. A complex phenomenon such as a war is always the result of many ‘smaller’ causes. However, of the four causes, the most obvious cause is option A, the invasion of Kuwait by Iraqi forces (lead by Saddam Hussein) on 2 August 1990. This was indeed the result of an oil crisis in which Iraq accused Kuwait of harvesting too much oil, thereby causing the global price of oil to drop (which affected Iraqi revenues).
