Staff doctors and nurses from Chicago wait for their next assignment at a evacuation hospital in Munich, Germany, on July 20, 1945 (Image/AP) World War II, the deadliest conflict in modern history, officially began in September 1939 when Germany invaded Poland. Two days later, Britain and France declared war on Germany. On 3 September, British Prime Minister Neville Chamberlain announced via a BBC broadcast that the United Kingdom would fight against Nazi Germany. While the invasion of Poland was the immediate cause, historians agree that deeper political, economic and historical factors made the war almost inevitable. The Treaty of Versailles...