Causes of World War II
Though the precise date of the start of the second World War is highly disputed, historians generally converge on 1 September, 1939, when Germany invaded Poland. There were several important factors that led to this, and these are also disputed.
The pretext for the German-Polish conflict started with a conflict over the German city of Danzig, which had been separated from Germany and made into a so-called 'Free City' but awarding oppressive conditions and rights in the Free City to Poland at the Versailles conference. Hitler, who had respected the former Polish leader, Pilsudski, and did not want war with Poland, initially attempted to negotiate Danzig's return to Germany. From January through March 1939, Hitler approached the Polish government several times with diplomatic overtures, seeking to resolve "the Danzig question" by negotiation.
Hitler's proposals included allowing Poland to retain the economic controls it already possessed and joining Germany in an alliance against the Soviet Union. Germany would gain direct political control of Danzig, her reabsorption back into the Reich, and Germany would be permitted to erect an extra-territorial railway and autobahn across the "Polish Corridor" to East Prussia.
British guarantee to Poland
Though negotiations at times seemed promising, they were eventually derailed when, on 31 March 1939, Britain gave Poland an unsolicited guarantee of Poland's borders and promise of support if attacked. This 'war guarantee' (the French already having mutual defence treaties with Poland) promised Poland that in the event of an attack on its territorial integrity, that Britain and France would militarily aid Poland against the aggressor. The guarantee had not been requested by Poland.
This 'blank cheque' had the effect of deterring Poland from further negotiations with Germany, convincing its leadership that it no longer even had to negotiate over the return of Danzig. The guarantee also solidified Hitler's belief that Jews were working to ensure that Britain and Germany were on a collision course to war. Indeed, Samuel J. Bullitt, who worked in the Roosevelt Administration and was of Jewish descent, had been working to convince Poland not to negotiate with Germany while also pressuring the British government to take proactive steps against Germany. The Jewish community in America and Britain was determined to drive Britain into a war with Germany, and used all of their financial and political leverage in order to bring about that very eventuality.
German invasion of Poland
On 1 September, 1939, Germany invaded Poland. As a result, two days later, on 3 September, Britain (with France shortly following them) declared war on Germany. What began and should have remained a localized conflict over the fate of a German city, Danzig, between two continental European nations, namely Germany and Poland, was now expanded by Britain and France into a Continental war involving all of Europe's major powers. In time, this European war would expand to include America and the Soviet Union, and eventually most of the nations of the world.