How to know the real history of what happened? Especially, when I read about a person there are multiple views on him. Some people have prejudice over him and others support him and every writer who writes about him might have biases towards the person. So, how do I judge if the person that I'm reading was really good or bad?
The problem is that history is created and perpetrated by humans, and it is then written by humans, studied by humans, examined by humans, presented by humans to humans.
The related problem is that the human is a stupid, selfish, blinkered creature with a hideously limited point of view and biases everywhere.
In history, the question is not whether something is biased. They all are. Everything is biased. There's no escaping that. The question is, instead, how is the source biased, and how does their bias affect their point of view? I refer you to my usual set of previous posts when asking about bias:
Also, see next post.