One of the biggest problems with political correctness is judging historical matters by the mores of today.
Many profess upset at the bombing of Dresden towards the end of World War II. We know the war ended in May 1945 but in February 1945 the final outcome was unknown. The dropping of the first atomic bombs is similar.
Slavery happened, but most forget that the Europeans did not land from their ships and rush inland to round up slaves, they were supplied by other Africans.
In WWI deserters were shot, but if you were guaranteed a place in prison, thousands may well have chosen that instead, but we have a campaign for them to be pardoned retrospectively.
Most "history" is now (re)written by those of a left wing agenda, with an honourable exception of Niall Ferguson, whom I can recommend, particularly his work on the British Empire.
Well, if "left wing" means "analytical" as opposed to "cheerleading" then yes, maybe. Ferguson has his own point of view, but it isn't that unusual. The empire could have been a lot worse, yes, but there were a lot of unsavoury things about it too, and downplaying the latter to praise it is going to get you a lot of approval from people who would like to overlook the problems. Taking the problems into account is just writing about what happened, not rewriting history.
The Dresden firestorm was the intended effect that area bombing was intended to create. It was simply one of the few cases where it actually worked (Tokyo was another), and had little to do with the detailed progress of the war. Dresden itself had relatively little importance to the German war effort and the industrial areas weren't targeted (as Freeman Dyson who was with Bomber Command staff put it, it had rapidly become clear that the planes of the time couldn't reliably hit any target smaller than a city). By February 1945 victory was more a matter of when not if anyway.
It's certainly arguable that it took WW1 to get an understanding of the effects of "shell shock", but since there now is a better understanding, retrospective pardons are a logical suggestion. Deserters generally weren't shot in WW2, but hey, somehow the Allies managed to win that one too.
As for slavery, yes it's important to note that it piggybacked off an existing practice. The availability of (in effect) a mass export market added a layer of brutality all its own though, and even with the mores of the time there were a good number of people capable of noticing the ethical problems involved.
Claims of "political correctness" are usually a red herring ...