Why did the US insist on invading Japan instead of blockading it in WWII?

Question

One of the reasons often used to justify the use of nuclear weapons is that the alternative strategy, firebombing and invasion of Japan, would have caused much more death and destruction for both Americans and the Japanese. But I wonder, why was an invasion the necessary alternative?

As I understand, Japan was running low on resources such as oil, rubber, and steel, even from the beginning of the war. If the invasion of the homeland looked so costly for both sides, why was it deemed necessary?

I'm not aware of any allies Japan could have counted on to supply it; why not maintain a blockade and wait them out? It seems that that would have cost less in terms of American casualties.

Answer 1

During the war the policy of the United States Congress and the President and the chiefs of the armed services was to attack Japan and Germany with the full and undivided power of the country until they surrendered absolutely and unconditionally. This was made abundantly clear at multiple points, including the joint Proclamation Defining Terms for Japanese Surrender issued after the Potsdam conference:

The prodigious land, sea and air forces of the United States, the British Empire and of China, many times reinforced by their armies and air fleets from the west, are poised to strike the final blows upon Japan. This military power is sustained and inspired by the determination of all the Allied Nations to prosecute the war against Japan until she ceases to resist....

....The full application of our military power, backed by our resolve, will mean the inevitable and complete destruction of the Japanese armed forces and just as inevitably the utter devastation of the Japanese homeland.

Proclamation Defining Terms for Japanese Surrender
Issued, at Potsdam, July 26, 1945 By The United States, England and China

Surrender or the US, British Empire, and China will use the "full application of our military power" to deliver the "utter devastation of the Japanese homeland." Is that clear enough? Minimizing casualties was not on the list of objectives.

Answer 2

Because only an invasion, or a credible threat of it, will have brought unconditional surrender. The latter let the Allies neutralise the strategic threat from Japan, by replacing their military dictatorship with a pacifist democracy and reducing the Emperor to a figurehead.

There's some possibility that Japan may have fought on, at least to defend the home islands, as evidenced by an attempted coup to prevent the acceptance of surrender, despite being nuked. Before the nukes and Soviet invasion of Manchuria, the government was actually unwilling to surrender. How much of the surrender was because of the nukes or because of the Soviets is up for debate.

On that note, there's the spectre of the Soviets rushing into Japan before the US, as they did in East Germany, and as they half-did in Korea. If the US was unwilling to invade, that's basically inviting the Soviets to take their place and gain a surrender favourable to them.

Besides, blockades aren't as great as you make it out to be. Starving and isolating an entire country doesn't exactly endear yourself to the population. We have at least two real-life examples of what happens: North Korea and Iraq between the gulf wars. Both regimes are/were stable and hostile as ever. Compared to them, the outcome for Japan was a miracle.

Answer 3

The United States already had crippled Japan with an embargo, however, they knew from other invasions in the Pacific that they wouldn't surrender, so the only options were to invade, or use the new nuclear technology, which did the trick.