Not only did Japanese cause 2,400 American lives, but also 37,000 killed Chinese in the Rape Of Nanking, and thousands more at Bataan Death March.
Just not having the bomb dropped, the war would have ended horrible.
Radiogram reporting the attack of Pearl Harbor
December 7, 1941, Japanese bombers and planes attacked a U.S Naval base near Pearl Harbor. In less than 2 hours, the U.S. Naval base was devastated, and more than 3,500 Americans were either killed or wounded.
Newspaper Entry
Hawaii was attacked by the Japanese without a warning or hints for Americans to be ready.
Pearl Harbor Insident
Japanese attacked the United States at Hawaii, December 7th 1941 which was a major event later called Pearl Harbor. This event motivated the United States to officially enter the war. (Link Above)
http://vimeo.com/33302620
A surviver of World War II tells his story of his experience on the attack that occured in Hawaii. The video link above also contains Roosevelt's speech to motivate men to go to war.
F.D.R's Speech:
To the Congress of the United States:
Yesterday, December 7, 1941--a date which will live in infamy--the United States of America was suddenly and deliberately attacked by naval and air forces of the Empire of Japan.
The United States was at peace with that nation and, at the solicitation of Japan, was still in conversion with the government and its emperor looking toward the maintenance of peace in the Pacific.
Indeed, one hour after Japanese air squadrons had commenced bombing in Oahu, the Japanese ambassador to the United States and his colleagues delivered to the Secretary of State a formal reply to a recent American message. While this reply stated that it seemed useless to continue the existing diplomatic negotiations, it contained no threat or hint of war or armed attack.
It will be recorded that the distance of Hawaii from Japan makes it obvious that the attack was deliberately planned many days or even weeks ago. During the intervening time, the Japanese government has deliberately sought to deceive the United States by false statements and expressions of hope for continued peace.
The attack yesterday on the Hawaiian Islands has caused severe damage to American naval and military forces. Very many American lives have been lost. In addition, American ships have been reported torpedoed on the high seas between San Francisco and Honolulu.
Yesterday, the Japanese government also launched an attack against Malaya.
Last night, Japanese forces attacked Hong Kong.
Last night, Japanese forces attacked Guam.
Last night, Japanese forces attacked the Philippine Islands.
Last night, the Japanese attacked Wake Island.
This morning, the Japanese attacked Midway Island.
Japan has, therefore, undertaken a surprise offensive extending throughout the Pacific area. The facts of yesterday speak for themselves. The people of the United States have already formed their opinions and well understand the implications to the very life and safety of our nation.
As Commander in Chief of the Army and Navy, I have directed that all measures be taken in for our defense.
Always will we remember the character of the onslaught against us.
No matter how long it may take us to overcome this premeditated invasion, the American people in the righteous might will win through to absolute victory.
I believe I interpret the will of the Congress and of the people when I assert that we will not only defend ourselves to the uttermost, but will make very certain that this form of treachery shall never endanger us again.
Hostilities exist. There is no blinking at the act that our people, our territory, and our interests are in grave danger.
With confidence in our armed forces--with the unbounding determination of our people--we will gain the inevitable triumph--so help us God.
I ask that the Congress declare that since the unprovoked and dastardly attack by Japan on Sunday, December 7, a state of war has existed between the United States and the Japanese empire.
The Japanese attack. 
Damage done to cargo ships.http://www.msnbc.msn.com/id/21578185/ns/us_news-military/
Paul Tibbets, the then thirty year old man who dropped the atomic bomb (The little boy) on Hiroshima. He qoutes that he doesnt regret dropping the bomb nor feel proud for killing those 80,000 people.
http://www.doug-long.com/hst.htm
Harry Truman's Journal Entries talking about his thoughts towards dropping the bomb. It also states his personal opinions.
(Below is an example of a journal entry written on his Japanese strategy)
6/17/45 Diary Entry:
"I have to decide Japanese strategy - shall we invade Japan proper or shall we bomb and blockade? That is my hardest decision to date. But I'll make it when I have all the facts."
[The next day Truman met with military representatives to discuss how the war against Japan should proceed. Truman decided at that meeting to have the Joint Chiefs of Staff go ahead with plans to invade Kyushu, the southernmost of Japan's four major islands. The planned invasion date was Nov. 1, 1945].
[7/16/45: The first atomic bomb was successfully tested. That night Truman, who was in Potsdam, Germany at a conference with Churchill and Stalin, received a brief secret notification that the atomic bomb test had "exceeded expectations". It's likely that Truman's diary reference on 7/17/45 to his "dynamite" refers to the a-bomb news, of which he had not told Stalin, from the 16th.]
Women Workers
During this war women had to work twice as hard. Women had to take over men's jobs so that men were able to go fight for their country. Women were now making steel for ships, cars and aircraft. Factories were either building up or expanding. Some women would also pledge in to the war. (Link on Picture page.)
Victory Garden
To also help out during the war time, government had rationed foods such as sugar, milk, meat, coffee, etc. Government had encourged American citizens to plant what they were callled " Victory Gardens" . Nearly 20 million Americans had helped out. For more information: http://www.livinghistoryfarm.org/farminginthe40s/crops_02.html
Child Speaker Audio
Even children understood and saw the need to help during this war.
Finally after loosing many life's on both sides, the United States and at Japan, Japanese surrender. The U.S dropping of the atomic bomb on Japan is justified because if it saved many American lives. It also brought WWII to an end.
