It's really phenomenal to think about how many people died in WW2. It's literally difficult to even imagine. And your numbers there are a bit off. Estimates tend to start more around 70 million. And I think that's leading to you low ball the potential death toll in future wars. In 1945 the entire world's population was around 2.4 billion. Nearly 3% of the world was killed or died as a result of WW2. The world's population today is 7.6 billion. A war of the same effect would have an expected death toll of around 222 million people. And that's probably substantially lowballing it as we have far greater ways of killing each other now a days, even if we take nukes out of the picture.
Even just back to those 70 million, let's say 73 million as that's where Wiki starts and it seems reasonable. Just imagine that. That's a 9/11 scale of death every single day for 24,366 days. Or a 9/11 scale event every single day for 67 years. That's again difficult to even imagine. And all of that death, with a population 1/3rd of ours today, was compressed into 6 years. Such lessons should never be forgotten, but in a way it's difficult to learn from such things when we really cannot even imagine death and destruction on this scale now a days.