Y'know, you really don't need to overcomplicate this one

Technically all 3

I fail to see how any of these 3 statements are incompatible or have more truth than the other.

After Russia wrapped up their European theater, as promised to the allies, they began to amass for a northern front with Japan. Two nukes, and the Japanese still resisted, until they realized they will be fighting a two front war with no resources to continue - surrender was the only option, and to the US, because the US actually followed Geneva Convention. Russia would have torn them asunder.