Why did the United States bomb Hiroshima and Nagasaki instead of accepting Japan's surrender or peace terms?

It's my understanding that there was much more that the Japanese wanted than just the right to have a 'nominal' Emperor. The Japanese still wanted to keep much of the land they had occupied - especially in northern China for the oil and other resources. They also wanted to keep a significant military and navy. Plus there certainly was a racial aspect on the part of the allies: only unconditional surrender by these Nip/Yellow Peril/slant eyed kamikazes would be acceptable.