Title: Political history of the world
Content:  World War II is generally considered to have begun on 1 September 1939, when Nazi Germany, under Adolf Hitler, invaded Poland. The United Kingdom and France subsequently declared war on Germany on the 3rd. Under the Molotov–Ribbentrop Pact of August 1939, Germany and the Soviet Union had partitioned Poland and marked out their "spheres of influence" across Finland, Romania and the Baltic states. From late 1939 to early 1941, in a series of campaigns and treaties, Germany conquered or controlled much of continental Europe, and formed the Axis alliance with Italy and Japan (along with other countries later on). Following the onset of campaigns in North Africa and East 
Title: World War II
Content:  It is generally considered that in Europe World War II started on 1 September 1939, beginning with the German invasion of Poland and the United Kingdom and France's declaration of war on Germany two days later. The dates for the beginning of the war in the Pacific include the start of the Second Sino-Japanese War on 7 July 1937, or the earlier Japanese invasion of Manchuria, on 19 September 1931. Others follow the British historian A. J. P. Taylor, who held that the Sino-Japanese War and war in Europe and its colonies occurred simultaneously, and the two wars became World War II in 1941. Other starting dates sometimes used for World War II include the Italian invasion of Abyssinia on 3 October 1935. The British historian Antony Beevor views the beginning of World WarII as the Battles of Khalkhin Gol fought between Japan and the forces of Mongolia and 
Title: World War II by country
Content:   The Empire of Japan was the leader of the Axis powers in the Pacific Theatre. Some scholars consider the outbreak of the Second Sino-Japanese War, which began when Japan invaded China after the Marco Polo Bridge Incident in 1937, to be the true beginning of World War II. This conflict merged with the world war following Japan's attack on Pearl Harbor in December 1941, which was immediately followed by a series of coordinated attacks on the U.S.-held Philippines, Guam and Wake Island; on the British colonies of Malaya, Singapore, and Hong Kong; and on the Kingdom of Thailand. During 1942 Japan launched offensives in the China, Southeast Asian, and Pacific Theatres of the war. By late 1942 Japan was on the defensive as the Allies reversed its earlier gains. The Atomic bombings of Hiroshima and Nagasaki by the United States, together with the declaration of war by the Soviet Union, convinced the Japanese government to surrender unconditionally on September 2, 1945. Many political and military leaders from Japan were convicted for war crimes before the Tokyo tribunal and other Allied tribunals in Asia.
Title: Europe
Content:   Two world wars and an economic depression dominated the first half of the 20th century. World War I was fought between 1914 and 1918. It started when Archduke Franz Ferdinand of Austria was assassinated by the Yugoslav nationalist Gavrilo Princip. Most European nations were drawn into the war, which was fought between the Entente Powers (France, Belgium, Serbia, Portugal, Russia, the United Kingdom, and later Italy, Greece, Romania and the United States) and the Central Powers (Austria-Hungary, Germany, Bulgaria and the Ottoman Empire). The war left more than 16 million civilians and military dead. Over 60 million European soldiers were mobilised from 1914 to 
Title: Key events of the 20th century
Content:  The First World War (or simply WWI), termed "The Great War" by contemporaries, started in 1914 and ended in 1918. It was ignited by the Assassination in Sarajevo of the Austro-Hungarian Empire's heir to the throne, Erzherzog Franz Ferdinand, by Gavrilo Princip of the organization "Young Bosnia," Bosnian Serbs' liberation movement. Bound by Slavic nationalism to help the small Serbian state, the Russians came to the aid of the Serbs when they were attacked. Interwoven alliances, an increasing arms race, and old hatreds dragged Europe into the war. The Allies, known initially as "The Triple Entente", comprised the British Empire, France, Italy, and Russia. Germany, Austria-Hungary, Bulgaria, and later the Ottoman Empire, were known as "The Central Powers". In 1917, Russia ended 
Title: Pact Ribbentrop - Beck
Content:  The author writes that by Poland not opposing Adolf Hitler in September 1939, the Second World War starts on April 9, 1940 by a German attack on Western Europe. After capturing Paris and defeating Belgium, the Netherlands, Norway, Denmark and France, on June 21, 1941, the Wehrmacht, together with the Polish Army, invades the Soviet Union. By the winter of 1941-1942, the Soviet Union ceases to exist. Poland and Germany divide its territory, but soon, mutual relationships deteriorate. Meanwhile, Germany keeps fighting the United Kingdom and the United States. The war is costly, and by 1944, all of the main units of the Wehrmacht are in 
Title: Causes of World War II
Content:   The causes of World War II, a global war from 1939 to 1945 that was the deadliest conflict in human history, have been given considerable attention by historians from many countries who studied and understood them. The immediate precipitating event was the invasion of Poland by Nazi Germany on September 1, 1939, and the subsequent declarations of war on Germany made by Britain and France, but many other prior events have been suggested as ultimate causes. Primary themes in historical analysis of the war's origins include the political takeover of Germany in 1933 by Adolf Hitler and the Nazi Party; Japanese 
Title: The War That Came Early
Content:  The series's initial point of divergence occurs when Spanish Nationalist leader José Sanjurjo avoids the plane crash that took his life in reality. While Sanjurjo's rule starts on a similar path to that of Francisco Franco, he later aligns Spain with the Axis powers. A second divergence occurs when British and French appeasement at the Munich Conference lead Adolf Hitler to decide that he should attack while his opponents are unprepared; he gets his casus belli when Konrad Henlein is assassinated by a fictional Czech nationalist. As a result, World War II starts in 1938 with a German invasion of Czechoslovakia rather than Poland, still drawing in Britain and France due to treaty obligations, with both sides far less prepared for war than they were in the real 1939.
Title: Western Front (World War II)
Content:  On 1 September 1939, World War II began with the German invasion of Poland. In response, Britain and France declared war on Germany on 3 September. The next few months in the war were marked by the Phoney War.
Title: World War II
Content:  the only two uses of nuclear weapons in war. World War II was by far the deadliest conflict in human history; it resulted in 70 to 85 million fatalities, a majority being civilians. Tens of millions of people died due to genocides (including the Holocaust), starvation, massacres, and disease. In the wake of the Axis defeat, Germany and Japan were occupied, and war crimes tribunals were conducted against German and Japanese leaders. World War II is generally considered to have begun on 1 September 1939, when Nazi Germany, under Adolf Hitler, invaded Poland. The United Kingdom and France subsequently declared war on 

Question: who started ww2 and how did it start?
Answer: Nazi Germany.