Hiroshima just happened to be a military and industrial target which was considered “best choice” by the military analysts

The estimation is that the bombing(s) in August 1945 stopped the war in its tracks and saved at least 1 million allied lives – including civilian lives which were being lost under the harsh conditions of occupied Asia. Experience in Iwo Jima indicated that the Japanese would keep fighting to the last man – any delay in concluding the war was therefore difficult to justify . By this time only unconditional surrender would satisfy the Allies which seemingly could not be obtained by any other means – the Japanese were given the opportunity to surrender before the deployment of the first bomb (code name Little Boy) – but did not – and were still trying to obtain some deal even after this bomb was dropped from the Enola Gay.

In such evaluations enemy losses are irrelevant – this is war not a game. The reality is that more people perished in the firestorms of Tokyo than were killed at Hiroshima or Nagasaki – but the delivery of such devastation by a single weapon was undoubtedly awesome. There was third bomb available but not deployed. The selection of Hiroshima as a target was largely arbitary – nagasaki even more so as it was not rthe original choice – but in the manner of a demonstration the target had to be one that had largely been undamaged in previous raids (Tokyo and Osaka were in ruins by this stage)

There is also the consideration that Congress had spent something like 25 billion $ US in today’s terms and wanted to know if the thing worked but that is rather different from being a necessity. There is no doubt that such a demonstration was also intended to impress upon the Soviets the new world order.