In 1939, on September 1, Nazi Germany invaded Poland.This period also saw significant technological advancements, with innovations in medical and military fields changing the world.After the war ended on September 2, 1945, with Japan's surrender following the atomic bombings, world leaders came together to create the United Nations, an organization aimed at promoting peace and international cooperation.As the fighting spread across most of the world--from Europe to Asia and Africa--cities were bombed, and people fled their homes, living in fear and anxiety.???