I don't know if Historical events should be changed, though some horrible and downright evil things have happened in the History of the World each of these events has a ripple effect to other events.
An example from my personal family history to explain this would be that during World War 1 my grandfather was wounded as a result of being shot by the enemy. This required medical treatment and time in hospital. It was while he was laid in hospital that he met my grandmother who was volunteering to visit soldiers without families to comfort them. This resulted in them marrying and having 5 children some of whom have children and grandchildren of their own. Though I am obviously not happy that my grandfather got shot during the war if he hadn't been my family history would have been completely altered.