Why couldn't the U.S. have simply left Japan instead of dropping atomic bombs in 1945?

Your idea is interesting....the US just declaring unilateral peace and just leaving Japan alone in Aug. 1945 since by then Japan had been knocked back to Japan anyway and was pretty much in a shambles and the Pacific again was free....BUT...for debate....the peril was great and impossible......At the time....

A.) Japan still had 1 million top troops under arms in their home islands and plenty of weapons for 1 million new troops.

B.) They made it clear even if the US declared peace they never would but would regain their strength and keep the war going against the US until Japan won.

C.) Japan still had another 1 million troops in cruel occupation of much of China and SE Asia and no intention of moving them.

D.) They still held in concentration camps all the US POW's they had captured.

E.) They were very close to developing biological warfare and would continue to do it.

F.) Japan still had great industrial capacity and if given a breather in 2 years could have challenged the US again.

G.) Even in a negotiated peace where Japan released the POW's and promised to give up biological/ chemical weapons and peace there would be no way to check if they did, and they would never leave China or SE Asia.

Japan had made it 'total war with no mercy and only Japan winning or nothing no matter what', from the beginning. Never gave up on that until after the 2 bombs dropped and the huge Russian invasion was underway.

The whole thing began with US interest in China. It would be better to think of the war in the Pacific not as an addition to WW II in Europe so much as a widening of the Second Sino-Japanese War. We could hardly leave the Japanese in China continuing to murder Chinese civilians at the rate of perhaps a quarter million per month. The alternatives from the use of the atomic bomb were the planned invasion, or simply continuing the naval blockade and aerial bombing campaign. Either of those options would have killed many times more Japanese than the use of the atomic bomb.

"Seems like the U.S. was not being threatened" (?)

Perhaps you are confused? Let's put a few things in perspective!

#1. August 2, 1945 (four days before Hiroshima) The Japanese Navy hospital ship Tachibana Maru boarded and captured with 1,500 healthy troops dressed in robes marked with red crosses on the sleeve. 30 tons of rifles, light machine guns, 75mm artillery shells, mortars, ammunition. The capture of the Tachibana Maru was the largest single capture of Japanese troops during the war!

#2. The USS Indianapolis, July 30, 1945 (6 days before Hiroshima) The very ship that carried the heavy detonating core of the Hiroshima bomb was sunk by a Japanese submarine and sank in 12 minutes, survivors lingered four days before discovery, only 350(?) survived from 1,400 (?) the largest naval disaster of WW2.

Japan had uprooted every pine tree on the island to distil wood alcohol to power Kamikaze aircraft, power speed boat Kamikaze craft,

Japan's military still controlled parts of North New Guinea, Borneo, Sumatra, Malaysia, Thailand , French Indochina, China, Manchuria, and a great many Pacific Island areas.

Left them WHAT? The Empire they had carved out of China, Southeast Asia, and in the Western Pacific? Why should they have been rewarded for their aggression?

American forces were not in Japan. The choice was Drop the Bombs or Invade.

1 Public opinion was too inflamed to accrpt that

2 The Russians were starting to attack the Japanese in the north. The US wanted a quick peace deal to stop the Russians gaining more territory

Wow, your ignorance of the history of the time is stupendous, and not in any good way.

In 1945, the US' military forces were NOT IN Japan. Japan started the war by attacking the US Fleet in Pearl Harbor, Hawaii, without bothering to declare war first. Once you start a war, you really have no standing to complain about it once you are losing it, and by 1945, Japan wasn't just losing, they had totally lost the war that they started. But, they were too frelling stubborn to face that reality, and thus surrender.

Thus, the US had to use more force to get them to surrender. The available choices were Atomic Bomb or invasion from the sea, and the invasion would likely have resulted in several million people being killed.

Thus, the use of the Bomb was the far more humane way to get Japan's irresponsible leaders to face their reality. It's their fault.

They weren't in Japan you idiot

American forces weren't in Japan.

You have no hope of arguing anything, as you seem to have no knowledge base on which to fall back upon.

As a general rule, you fight a war to defeat your enemy. You know they are defeated when they admit it. They aren't until they do.

From a practical perspective, they lost all hope of beating us on June 4, 1942. But on they fought. Your alternative would be to let them keep fighting a war?

War only takes one side to engage in. Peace requires the active participation of everyone. Japan, despite all the revisionist claptrap, wanted to keep fighting. They refused to be starved out (fifteen months of an airtight blockade on an island nation with insufficient foodstuffs to adequately feed their population), refused to acknowledge having lost every battle since Coral Sea, which was a draw, refused to stop massacring the Chinese, refused to treat prisoners humanely, and continued to fight suicidally You don't leave someone who wants to fight you alone. You end it. If you are humane, you end it as swiftly as possible. We did.

you'll never ever ever believe why, never !!!

The U.S. was pulled into that war by Japan and the attack at Pearl Harbor. Up until then America was trying to stay out of the war. Since Pearl Harbor America began taking the surrounding military bases in the Pacific from Japan but they still held strong. America thought they needed something big to stop them. The pro behind dropping the bomb was that it scared Japan's leaders into an immediate surrender because it was a weapon no one had seen before. the con behind it was that the bomb killed military and civilian alike and also introduced the world to nuclear weapons.