History is not study of past. History is a study of recorded passed. It is not possible to know every event which have happened before now to everyone, everywhere, at any time. What we could know is based on survived evidence such as pass newspapers, documents, articles, videos, etc.
History is not like other social sciences which can do the experiment directly and make conclusion. For example, economist can collect the data like GDP, and to predict future economy. History study is only based on the evidence that left behind from the past because historian cannot take time-travel to see what was happened, and those evidence are very limited.
Furthermore, those evidence which consider to be useful was usually created by authorized man, and because of the censorship. Those survived evidences usually were not complete story, even more, untrue. It only tell us what the “authorized man” thought what was happened or what he want others to think what happened. Therefore, it is hard to tell that what we learn from the history is the facts about the past or the story that the people in the past want to tell us.