Objectivity is possible. But no-“body” is objective. That is, we all have our biases. It’s a good goal to strive towards a kind of objectivity, but attainment is unlikely imo.
Truth lies inbetween the tussle and hassle, the push and pull of frustrated “almosts”. It’s wispy though, rarely firm.
However, when it comes to “who” did what to “whom” things, it’s necessarily subjective. It’s subject vs subject. What’s the objective truth between subjects? You might get a third party view which will likely see both parts a little better than each individual one but there’s always subjective elements when dealing with subjects.
That’s why a unified World History will likely be impossible.
Shame though. I’d read it.