You want it detailed? Ok fine. Some historians argue that W.W.2 was Hitler's personal war, that he had been planning and preparing for it before he came to power. During the period of 1935-1939 Germany broke all the laws implemented by the Treaty of Versailles. Rearmament; the moving of soldiers back into the Rhineland; the unification of Austria, the Sudetenland, and soon after the entire Czechoslovakia, and Poland with Germany all caused much tension in Europe, hence the war had started.

The fact they went from a third world country to the most powerful nation militarily in a few short years was a pretty good indication.

When Hitler took full power in 1934 he began to secretly re-arm Germany with new jobs being created in all sectors of work Germany became a superpower at the outbreak of war in 39 only 38000 people were unemployed. Politically Hitler anounced his intentions by breaking several treaties, Versailles (which prohibited rearmament) and Locorno which was suppose to settle the issue of national borders. He also abandoned the league of nations set up after WW1 to ensure lasting peace and in aiding General Franco in the Spanish Civil War (37-39) Hitler practiced for war. Which caused much concern in France and Britain. Then in September 1939 Hitler annexed Poland who had a treaty with Britain and France forcing them into WW2. Summary .Germany becomes superpower .Treaty Versailles Broken (Rearmament) .Treaty Locorno Broken (union with Austria/Rhineland) .League of Nations Failure .Spanish Civil War (practice) .Annex of Poland = WW2

"The Gathering Storm" by Winston Churchill.

Some interesting answers here. But none answer the question "WHY"? There is a reason for everything, and the events leading up to WW2 are wrought with unanswered questions. The first of which is the Versailles Treaty. Germany was starved into submission by illegal blockades by Britain. The subsequent Versailles Treaty violated international law by denying Germany its right to sovereignty. Germany was also denied a military large enough to protect itself beyond its immediate shoreline. They were forced to reduce arms while the United States and Britain continued to build up their own militaries. In 1933, the Jews declared war on Germany. By 1935, Roosevelt was stirring up conflicts with the hopes of getting into a war with Germany. In 1938, PM Chamberlain returned to Britain as a hero when he averted a war with Germany - only to be chastised by Churchill because he backed down. Hitler tried to avoid was many times - Britain spat on every attempt. The invasion of Poland was set up by Britain. Poland's leader, Edward Rydz Smigly was a warmonger like Churchill but lacked the military to go up against Germany on his own. The Anglo-Polish Pact between Britain and Poland gave Smigly a false sense of courage and he provoked Hitler into an attack. But Britain never responded as promised - they left Poland hanging out to dry. They never intended to keep their word - they only wanted Poland to provoke a German attack so they (Britain) would be justified in declaring war on Germany. Of all of the leaders involved at the time, Hitler was the only one who had actually fought in a war - the rest sat in their ivory towers calling the shots. War is a political concern facilitated by those who don't have to do the actual fighting. Anyone who has been involved in a war surely has no desire to go through it again. I think people should take time to reflect on what exactly happened, who pulled the strings, and why.