By the fall of 1944, American military leaders realized that Japan would be unwilling to surrender. Vicious battles between the two sides, on several Pacific islands, convinced military planners (like General LeMay) to take drastic measures.
On the 24th of November, 1944, B-29s began to regularly drop bombs on Japan. Tokyo, a city whose buildings were mostly made of wood at that time, was a prime target.
When American pilots dropped incendiary bombs, blazing fires killed people and leveled cities.
This clip - from the documentary "World War II Battlefront" - features a segment on "The Last Stronghold (November, 1944)." It is not easy to watch.