I have a hunch that we talk more about the bombing of Hiroshima and Nagasaki because those deaths happened all at once, then left many people ill and poisoned the environment. But I'm wondering if the bombing campaigns in Germany, france, or great Britain actually killed more civilians.
The Soviet Union had c. 10 million civilians killed as a result of crimes against humanity; China, c. 7-8 million, and Poland, c. 5 million.