It occurred to me that the devastating power of wildfires would make a potent weapon. Has any army ever used large region engulfing fire to any effect in war?
edit: Its amazing to me that throughout history when large scale weapons of mass destruction were few and far between that forest fires didn't come into use very often. I know of crops being burned so I have to believe the knowledge base and tools were there.
The Japanese tried to do this in WWII, by using balloons equipped with incendiary bombs. The target was the northwest of the US, and the goal was to start fires to hurt the US war effort. The balloons were able to reach the US with their payloads, and they even got as far east as Detroit. They made landfall all the way from California to Alaska.
The damage, though, was quite low. There was only one attack that was lethal, killing a pregnant woman and five children. The balloon was already on the ground when they approached it, and it exploded. Other damage was very slight, though it did momentarily affect a Manhattan Project site. In short, the attempt was a near complete failure.
Best example of this in modern(ish) times is in Vietnam when napalm was used constantly and engulfed large part of the forest if the weren't as wet. Napalm was dropped to not only kill and burn out hostels but to also cover retreats and stop advances dead in their tracks. Lastly, the napalm being so hot when man were hit they steamed with so much agony it lowered the morale of Vietnamese soldiers.
Cleomenes of Sparta defeated an argive army in 494BC, driving the survivors into the forests around argos. Then he burnt the forest down killing the remains argives (herodotus book 5).
Funny ending to the story is that having defeated Argos, he ordered his men home, rather than take the city. A prophecy told him he would conquer argos and having burnt the forest he believed the prophecy had been fulfilled by his 'conquering' of the forest. Cleomenes was a bit crazy.