Objectivity isn’t meant to be a destination in the sense that it’s a place that one’s reporting can arrive at. It’s meant to be a process, one that can never be executed perfectly, but one that has the effect of improving the final product over what it would otherwise be.
As for your question, “when did WWII start?” The answer is that it’s an objective fact that there are a number of events that arguably mark the beginning of the war, all of which have varying degrees of merit. Complexity, or the fact that there is no one right answer to a given question, doesn’t mean that we have to throw out any effort at objectivity. It just means that we have to dig deeper.
The country is far more polarized than it has been since the 1850s and 60s. This is an objective fact.