July 16–August 5, 1945
Japan faces an ultimatum and converging threats
After the Trinity test, Allied leaders issue the Potsdam Declaration calling for Japan's surrender. Japanese leaders remain divided over acceptable terms while blockade, conventional bombing, invasion planning, and expected Soviet entry frame the crisis. The atomic missions are prepared on Tinian.
WHAT TO NOTICEThe decision occurs within several simultaneous military and political pressures; the map cannot assign one cause in advance.