Here's a few alternatives the other side uses, details at link:
Argument 4: There Were Alternatives
Alternative 1: A Demonstration of the bomb
Alternative 2: Wait For the Russians
Alternative 3: Let the Japanese Keep Their Emperor
Alternative 4: Continue Conventional Bombing
If we sat still and waited them out over a few decades (OK, maybe like 50 years), Obama could have used drones and their missiles to take out the Imperial general staff,
I’ve probably read that before (I don’t know why they put “Let the Japanese Keep Their Emperor” in there, since that was done - which is where our biggest mistake in WW1 in not allowing Germany to keep the Kaiser in place, even as a figurehead, which might’ve halted Hitler from rising to power).
Since we defeated the Germans first, we won’t know 100% whether we’d have used the bombs against them (however the Dresden bombings point to that we probably would’ve) had Japan capitulated earlier.
As for the Russians, as I stated earlier, allowing them in would’ve seen them demand a substantial chunk of Japan to Sovietize (as with East Germany and everything else behind the Iron Curtain). A divided Japan, free and Soviet, would’ve led to a Civil War similar to Korea and Vietnam, and my gut says Japan may have fallen to the Communists.
Conventional bombing ? They could’ve continued that, yes, but I think it would’ve merely resulted in stalemate. We were going to have to invade and subdue. You can’t control a country until your people are on the ground.
Let’s face facts, Americans were weary by August 1945, after taking care of Nazi Germany, they wanted a swift end in the Pacific Theater. Moving our men from Europe to the Pacific to join the ones already there was a difficult prospect. Had Truman sat on the bombs while continuing to play things out conventionally (while hundreds of thousands of casualties were racked up, American military and militarized Japanese civilians), the public would’ve lynched Truman and the Democrat party would’ve been obliterated (”Truman lied, millions died”).
Truman had no choice. The war had to be ended in Japan by using any means necessary that kept American casualties to a minimum. Demonstrations of the bomb would’ve been pointless. Hiroshima alone should’ve forced surrender, but it didn’t. Even Nagasaki almost wasn’t enough. If saner heads hadn’t prevailed in Japanese leadership realizing we were prepared to turn Japan into a sheet of glass from stem to stern, it’s difficult to ponder how much further we’d have had to go.
As for it being used as a warning to the Soviets as well, consider it a plus. Alas, they utilized more underground methods in their cold war against us (for which we’ve been reaping their successful results in recent decades).