Assuming that this is referring to the same list of options that was posted before with this question, <span>the correct response would be the transcripts of deliberations between the Americans in the war room leading up to the invasion, although these are classified. </span><span>A recorded conversation between Iraq's generals the day before the invasion</span>
I think the best source that would be best helpful for this historian is the transcripts of the Americans in a meeting which leads to the invasion. With this source, the historian can clearly hear what really happened and he can understand the causes.
