Final answer:
President Truman justified the use of the atomic bomb to save American lives and end the war swiftly. Demonstrating American military power and securing a favorable position in post-war negotiations may have also influenced his decision.
Step-by-step explanation:
President Truman decided to use the atomic bomb to end the war against Japan. The reason he used to justify this decision was to save American lives and bring a swift end to the war. He believed that dropping the atomic bomb would be a more effective strategy than a conventional invasion, which would have resulted in a higher casualty count. Another reason that might have influenced his decision was the desire to demonstrate American military power and secure a favorable position in post-war negotiations.
Learn more about Reasons behind President Truman's decision to use the atomic bomb in ending the war against Japan