For this essay, and for any essay, the thesis statement has to come from the process of reading. For example, you are reading about the Cuban Missile Crisis, and all the events that surrounded it, and you suddenly think to yourself, "I realize now that two main factors were at work to make this happen: XXXXX and XXXXXX. But I don't see the Cuban Missile Crisis explained in terms of these two factors in any of the articles I have found, so I am going to write my own article to contribute this idea, now that I am something of an expert about the subject because of all the reading I have done.
Read 5 articles about it, and make a list of ideas! I'll help you turn one of them into a good, "arguable" thesis statement.