Which of the following eventually led germany to start world war ii?

Germany's invasion of Poland was a key factor in World War II starting, amongst rising tension in Europe. 

The Treaty of Versailles, that ended the first world war, is perhaps the most controversial peace treaty in history; ‘many have judged it to be too harsh and others have judged it to be not harsh enough.’[2] Germany and the other defeated Central powers lost territory, had their military forces limited and were obliged to pay reparations. Germany was especially treated harshly. The German public was outraged when the Treaty’s terms were publicized because they believed that Germany had neither started the war nor been decisively defeated on the battlefield. The Treaty was treated Germany as if had been conquered and they felt that was both their country unfairly and inaccurate. Germany lost about one-fifth of its territory as a result of the Treaty. Overnight millions of Germans became citizens of other countries, such as Poland. The Treaty legally limited the size and scope of the German armed forces which was intended to prevent that the country from starting another war. The National Socialists benefitted from the harsh terms of the Treaty of Versailles helped the rise of the Party . It allowed them to not only justify their aggressive policies but portray Germany as the true victim of the Great War.[3]

In the 1930s, Europe was a divided continent. There were still bitter disputes over borders. The Treaty of Versailles had redrawn the border of Europe but it seemed to have satisfied no one.[4] These ongoing disputes meant that the political class still regularly used nationalism to retain power. There were almost no functioning democracies in Europe at this time and there were many military dictatorships. The continent was also divided between the left and the right. Almost every society was internally divided between communists and socialists and those who opposed them.[5] Then in many countries fascism had made great strides often because of a fear of communism. Europe was unstable and it seemed likely that the continent would descend into another conflict. This was to occur in 1939 and it was caused by the ambitions of the National Socialist government in Germany and its extreme ideology.