Well it's tricky to define "war" exactly. I mean technically the US hasn't been at war this entire time, and we're not at war with any specific government (mostly because they're either A) not organized, or B) the Taliban who we don't want to recognize as legitimate).
Considering all the firebombing that went on during WW2, I think the definition of a "civilian target" is something that doesn't directly hurt military capability. IE, people figured that burning down a whole city that built tanks was okay, and blowing up houses was fine if you expected that it was just troops quartered in them, but you didn't blow up a house with civilians in it, you chase them out first. Transport networks are fair game because they move materiel, but you don't, like...blow up a school bus factory regardless of if there's civvies in the building at the time or not, because that's kind of a dick move. If you're aiming for a strategic target like a rail depot and there happens to be a school next door, well, they'd better hope they were smart enough to evacuate before the bombs start dropping because despite your best efforts one might go off target and that's too bad but not your fault. If your enemies don't like collateral damage, that's why they sue for peace.
A guy who sneaks into your country and blows up a mall is a terrorist, a guy who sneaks into your country and blows up an ammo factory is by definition not, even if people get hurt either way. Enemy soldier yes, shoot on sight yes, but terrorist no.