The two dates most often mentioned as “the beginning of World War II” are July 7, 1937, when the “Marco Polo Bridge Incident” led to a prolonged war between Japan and China, and September 1, 1939, when Germany invaded Poland, which led Britain and France to declare war on Hitler's Nazi state in retaliation.
World War Two in Europe began on 3rd September 1939, when the Prime Minister of Britain, Neville Chamberlain, declared war on Germany. It involved many of the world's countries. The Second World War was started by Germany in an unprovoked attack on Poland.
