You should read up on Operation Downfall. The proposed invasion of the Japanese mainland. Conservative estimates had 200,000 US casualties and 5 million Japanese dead.
If anything, that was conservative...and didn't account for the certain mass famine that winter. Just the Army was expecting more than 1000 casualties per day. It also didn't account for the fact that all Allied POWs were to be killed in the event of an invasion.
Propaganda designed to cover up Truman’s war crime.
Did you ever ask yourself, why do we need to invade?
Because they would not fucking surrender.
Japan was defeated. It had no defense from air attacks that occurred in daylight every day and it's navy no longer existed as a viable force. The Bushido holdouts were desperately trying to negotiate reasonable surrender terms that included not executing the Emperor but the only president not to have graduated from college and president for about four months didn't have a freaking clue. The eggheads were dying to use their device and Truman gave the O.K.
The only terms they deserved were, "If you ask really nicely, we will not wipe you out to the last man, woman, and child." Note that even AFTER the two atomic bombs, surrendering damn near got Hirohito assassinated!