Conceptually, would it be useful for you to think of events leading up to the war, starting with the assassination, as distinct from the war itself?
This depends (on the user, the use case, the goal etc).
For example, if I was using the AT to study history, I would want to see the official start and end dates of the war on the timeline just so I can access the basic facts at a glance.
AT’s timeline already distinguishes when a parent event contains child event that has an earlier start date with the thinner line (which I really like):

This will help clue the user that, conceptually, there were relevant events happening before the official start date of the war.
Another example: I’m using AT to keep track of my employment history. I create an event for each position I’ve held, and I’m currently using the first day on the job as the start date, and the last day on the job as the end date. However, nested within that event are events like, when I applied for the job, when I got interviewed, when I got the job offer etc, which all happened prior to the first day of the job.
When I look at the timeline, I want to see the date range and/or duration of when I was actually on the job first and foremost (especially if I have the child events collapsed), and if I want to see more details pertaining to that job, I will expand the event.
I’m sure some prefer otherwise, and this might even depend on an event-to-event basis on the same timeline, but that’s why I mentioned I would like to have the option to always see the start and end dates of the parent event. It could simply be a checkbox in the “Date options” button in the inspector tab once you select a parent event.