Well obviously in modern day Civilian Casualties still happen but they're more talked about in a politically correct way when it happens.

Then I'd say you'd drop back towards the 70's and Vietnam and Cambodia where the American's just seemed not to give a fuck, they would drop napalm over towns and in Cambodia they built cities for the people to be taken to to avoid the spread of communism in villages and then to convince them to move to the cities they just bombed them (while not at war)

Then you drop back to WW2, you've got the air raids in the UK and Germany causing civilian deaths. Obviously you've got Hiroshima and Nagasaki (However I personally believe this was completely needed and I've wrote many essays on the topic if you want me to go into more detail about the two atomic bombs and why I think it's completely justified do let me know.) The Nazi's obviously did the holocaust which is mass extermination of civilians for different reasons to the normal once of wars, discrimination based reasons.

Then I'd say we drop back to WW1, where I personally don't remember much off the top of my head about civilian casualties I think WW1 can be considered as fairly lax for the deaths of civilians but it is an anomaly for deaths caused directly by attacking civilians directly, there was still 6.5 million civilian deaths in ww1 which mostly comes from the ottomans and the blockading of Germany causing malnutrition and deaths by starvation however in the grand scheme of things 6.5million civilians is 2.5million more than the Axis forces lost in WW2, even though the Axis forces lost 1/11th of the civilians that the Allied forces lost. So in comparison to WW2, WW1 was very small on civilian loses (OBVIOUSLY STILL A LOT)

Then we drop out of my in depth area of knowledge but if we go back to times like the Mongols we're looking at raping, pillaging and then killing them, meaning that you're look at Khan's regime just wiping out civilians on a mass scale.

So overall I think it's toned down and become less taboo, but then again most of war has toned down the modern era but there is still civilian deaths now just it's more frowned upon. Cambodia and Vietnam would be anomalies of complete extermination of civilians intentionally by the American's and WW1 as an example of very few Civilian deaths in comparison to other wars due to the trench warfare stalemate of that type of war.