What kind of research or validation can be done on the concept of established history?

That is what I am trying to ask. What would a research find out about established history? There is no way for I or you to deny that the World War I took place even though we did not see it happening. The historical record about it that we have today is itself based upon the already established fact that such a war took place. Similarly, no one can deny that there were Greek philosophers by the names of Plato and Aristotle, even though none of us ever saw them. Any historical record that we have today about them is also based upon the “established” fact that they existed.

What is there to research about the concept of established history? Established history refers to those historical events that cannot be refuted (i.e. they are established) because they were witnessed by a large body of people and then transmitted to us generation after generation by such a large number of people that it is inconceivable for them to be lies.