This post makes an extremely important and very very very poorly understood point. You are absolutely correct that whilst the conventional wisdom is that the US nuked Japan to avoid the loss of 500,000 lives invading the mainland the historical record is rather different. Recent scholarship has made this plain. For those interested I recommend starting with Gar Alperovitz's 'The Decision to Use the Atomic Bomb.'
On a point of detail, ironically it isn't true that 'the only casualties were Japanese." In Nagasaki there were a large number of conscripted foreign workers as well as the native Japanese population (mostly women and children).
Another good point about the firebombing. The US and UK airforce leaders were clear that if they lost the war the 1000 bomber raids onto civilian targets would likely be classified as war crimes and that they personally would be tried as war criminals.
You're definitely right that it was a war of decimation and sheer destruction (eg the fire bombing). It was a fight to the death. It's what makes a war like that so damn scary, the gloves literally come off. WW1 of course had plenty of that as well (chemical weapons). The civilian population required to support the industry necessary to build the war machines are part of the targeting if your intention is to survive that sort of conflict and stop the opponent's ability to produce more tanks, planes and weapons.
On a point of detail, ironically it isn't true that 'the only casualties were Japanese." In Nagasaki there were a large number of conscripted foreign workers as well as the native Japanese population (mostly women and children).
Another good point about the firebombing. The US and UK airforce leaders were clear that if they lost the war the 1000 bomber raids onto civilian targets would likely be classified as war crimes and that they personally would be tried as war criminals.