Japan was already badly weakened. The atomic attacks and Soviet entry added different pressures that helped bring the leadership to surrender.
By summer 1945, Japan had suffered military defeats, attacks on shipping and heavy bombing of its cities. Blockade means preventing supplies from reaching an enemy. This loss of supplies and conventional bombing, using non-atomic weapons, weakened production and the ability to fight. The United States then used atomic bombs on Hiroshima on 6 August and Nagasaki on 9 August. Their devastating destructive power and mass loss of life added an immediate threat of further destruction.
The Soviet Union had fought Germany as an Ally but had not yet joined the war against Japan. Japanese leaders hoped it might act as a mediator, helping negotiate better surrender terms with the other Allies. Instead, the USSR declared war on Japan on 8 August and attacked Japanese forces in Manchuria from 9 August. Japan now faced another powerful army and lost this hoped-for diplomatic route.
Japanese leaders disagreed about surrender. Emperor Hirohito intervened in favour of accepting it, helping resolve the deadlock. Surrender was announced in Japan on 15 August and formally signed on 2 September. Earlier defeat explains why Japan was weak; the August shocks help explain why the decision came then. Historians differ over the relative weight of the bombs and Soviet entry, so explain their distinct effects rather than presenting one disputed cause as the settled answer.
Worked example: Separate loss of strength from the decision to stop
Japan had been weakened before August, but its leaders had continued the war.
- Shipping losses, bombing and defeats reduced the supplies and forces available to keep fighting.
- The atomic attacks threatened further destruction. Soviet entry added military pressure and removed hopes of Soviet help in negotiating terms.
- These pressures met a divided leadership. Explaining the final decision requires those immediate effects as well as the earlier loss of strength.
Watch out for this
Japan signed its surrender immediately after the Hiroshima bomb.
Hiroshima was on 6 August. Further shocks and decisions followed; the announcement was on 15 August and the formal signature on 2 September.
Check your understanding
Why is Japan's surrender better explained by connecting several pressures?
- Japan's earlier military weakness proves that the leadership had already decided to surrender before August.
- Soviet entry mattered only by adding troops; Japan could still rely on the USSR to mediate on its behalf.
- Earlier losses weakened Japan, while atomic attacks and Soviet entry added destructive, military and diplomatic pressures on its final decision.