Question

Why is ancient history helpful to our society today

Answer 1

Because something which in ancient history is similar to today.

Answer 2

History repeats but we don't seem to be able to learn from our mistakes. Some also think that past actions can be predictors of future events-see probability and the roll of a dice.
Knowing our ancestors can give us an incite as to how and why we became as we are.
A study of past events can lead to better outcomes in the future - military tactics are partly based on this premise.
If we study each step of a process we can go back to see where we made vital mistakes - medical progress, thalidomide - crop development, can't remember this specific case but some cross cultivation failed badly and in a deadly manner (could have been done safely with gene splitting).
To be continued.................
again and again until we get it right.