September 17, 1939 The Soviet Union attacks Poland, more than two weeks after Nazi Germany launches its assault. These events trigger the beginning of World War II

September 18, 1961 Swede Dag Hammarskjold, Secretary-General of the United Nations, is killed in a suspicious plane crash in Northern Rhodesia (now Zambia). He was on his way to negotiate a ceasefire in the Congo. He received the Nobel Peace Prize in 1961.

September 19, 1955 Presi