What are 3 reasons that support why the United States justified in dropping the atomic bomb?

For Japan?

Explanation:

If it was for Japan, the U. S was soldiering on towards the end of a dark period of human history that had seen the single most costly conflict (in terms of life) in history, and they chose to adopt a stance that seemed to limit the amount of casualties in the war, by significantly shortening it with the use of atomic weapons.

It was certainly a reasonable view for the USA to take, since they had suffered the loss of more than 418,000 lives, both military and civilian. To the top rank of the US military the 135,000 death toll was worth it to prevent the "many thousands of American troops [that] would be killed in invading Japan" - a view attributed to the president himself.