Posting again:
Historians work to methodically dissect the past to help us understand the present and avoid making similar mistakes in the future.
The base job of a Historian is to break down a historical events into parts to understand how the historical event or historical arc could have occurred as it did. This could range from "Why did the Japanese bomb Pearl Harbor" to "Why did the Union win the Civil War"
Each question has answers that can help future generations understand the implications of their actions.