To end the war quickly and to avoid even more bloodshed had the US landed in Japan. Japan swiftly surrendered thereafter.

disregard for innocent human life?

K-Rex's answer is the "official" reason but the truth is that the war was lost and the Japanese had already approached the Russians to use them as a go between for negotiations for surrender with the Americans. The Americans had spent about 2 billion dollars on R&D for the A-bomb and they were sure as hell going to use it one way or the other. They also wanted to send a message to Russian, China and other countries that the US was now going to be Number 1 so don't mess with us. There is no credible evidence that the bombs saved more lives than it took. 80,000 people died immediately or a few days following the blast, almost all of them civilians, women and children. Also, radiation took it's toll over the years on survivors. How horrible to unleash this terror on the world. Truman should have been ashamed.

Japan was on track to fight to the last man, woman and child. That was proven on some of the islands were all the men fought unto death and the women and children jumped off high cliffs. We would have had to land our Marines on the Japanese Island and fought from shore to shore killing Millions of people including our own troops. The bomb (although now some call it inhumane) saved millions of lives. Truman made the decision and he was one presidnet we had who was not wishy-washy. He made hard decisions and stuck to them. I am old enough to remember the day Japan bombed Pearl Harbor.

To prevent the need for a full scale ground invasion. We were convinced by experience and the rhetoric of the Japanese that they will fight to the last man, woman, and child.

They were told to end the war. Repeatedly. They refused. Threatened another attack like on Pearl Harbor. It was a preimptive strike. If they had stopped it wouldn't have happened. They were warned about the nuke.

cause america rules

Pearl Harbor need I say any more

To end the war. The "official" reason was retaliation for the bombing of Pearl Harbor.

slim746, i would bet you are a liberal democrat, correct? you see this is the difference between democrats and republicans. the democrats tend to think that our country is evil in all its applications of military and its rulers are all the devil,at least when its a republican in charge. republicans tend believe that our nation strives for peace and justice in its use of military power. unfortunately, history would say that most peace is only had on the other side of conflict,something you liberals just would never get. you think we should have just reasoned with japan after the pearl harbor attacks. or perhaps we where wrong to help the Europeans fight Hitler. I mean its not our country and its only millions of people being exterminated right.if we hadn't helped them the world would likely be a very different place right now. The atomic bomb was the only way to win against the Japanese. they would have indeed fought to the death with every last man woman and child . how many people do you think would have died in that one. the bombs being dropped was actually the most moral way to win the war. innocence people die in every war its a very sad truth that cant be avoided.

One of the big reasons was simply that an invasion of Japan itself would have taken a long time and there would be major loss of life. There were probably other reasons, but that was the big one.

The first bomb that was dropped basically ended the war to save American lives. We stood to lose thousands of infantry lives otherwise. Some believe that the second bomb was more to study the effects of the "bomb" and was literally overkill but was necessary to save American lives in the end.