- Continued Allied Bombing: Without the use of atomic bombs, the Allies would have continued their conventional bombing campaign of Japan. This would have led to further destruction and civilian casualties but might not have been enough to force Japan's surrender.
- Invasion of Japan: An alternative to further bombing would have been an invasion of Japan by Allied forces. This would have been a costly and potentially protracted operation, with Allied casualties expected to be in the hundreds of thousands. The invasion of Okinawa, which occurred in April 1945, provided a preview of the challenges and casualties that an invasion of the Japanese mainland would entail.
- Prolonged War: The delay in Japan's surrender would have prolonged the war and resulted in increased suffering for both Japan and the Allies. Millions of lives could have been lost, not only in combat but also due to starvation, disease, and other disruptions caused by the ongoing conflict.
- Soviet intervention: In the absence of a swift end to the war, the Soviet Union might have taken a more active role in the Pacific theater. Soviet entry into the war could have changed the power dynamics and potentially increased the risk of further escalation.
- Diplomatic Pressure: As the war continued, diplomatic efforts to pressure Japan into surrender would have likely intensified. These could have involved additional economic sanctions, naval blockades, and ultimatums. However, Japan's leadership had consistently expressed determination to fight on, so the effectiveness of diplomatic pressure alone is uncertain.
Ultimately, the decision to use atomic bombs was incredibly complex and remains controversial. While it brought about a rapid end to the war, it came at a substantial human cost and raised profound ethical and humanitarian concerns. Counterfactual scenarios, as described above, offer insight into alternative possibilities but have inherent uncertainty due to the complex and unpredictable nature of historical events.