President Harry Truman believed unconditional surrender would keep the Soviet Union involved while reassuring American voters and soldiers that their sacrifices in a total war would be compensated by total victory. Disarming enemy militaries was the start; consolidating democracy abroad was the goal.

Why did the Allies demand unconditional surrender?

The Allies also hoped to prevent any public debate over appropriate surrender terms and, above all, wished to prevent Germans from later claiming that they had not been militarily defeated, as Adolf Hitler did after the 1919 Versailles settlement of World War I. ...

Why did Japan actually surrender unconditionally in World War II?

Nuclear weapons shocked Japan into surrendering at the end of World War II—except they didn't. Japan surrendered because the Soviet Union entered the war. Japanese leaders said the bomb forced them to surrender because it was less embarrassing to say they had been defeated by a miracle weapon.