Remember that the history we know is not presented always in an objective way, it is important to always have in mind that it's written by certain people in certain contexts. That means they had been affected by ideas of their times or the historic processes occuring at that moment. Winston Churchill demonstrated this with his famous phrase: "History is written by the victors".
It is the historian duty to present the historic events in the most objective way he can. One way to do this, is by consulting multiple sources of information on the topic he is interested. In this way different points of view and different possible causes to the topic can be found. As a consequence, we will be aware that the important events in history are not simple and that nothing is black-or-white.
