What were the reasons for Germany going to war again in 1939?
The occupation of the Ruhr and the excessive fines imposed on Germany by the victorious allies after ww-1, set the conditions to launch Hitler into power. Hitler gained the miliarys support by enlarging it. He gained the industry leaders and the peoples support when he refused to pay any more reparation penalties for ww-1, which fueled the growth of industry and put millions back to work. Hitler restored the German peoples pride. Hitler then rode the momentum and not only started reclaiming lost territory from ww-1 but started his 1,000 year Reich. Hitler and Stalin both shared plans for future expansion. The proof lies in the "then secret exchange program" between Hitler and Stalin during the 1930's. German aircraft and tactics were finetuned while conducting prohibited training on Russian Soil. In exchange the Germans provdided technicians, Officer training, and shared technology. In the opening days of WW-2 they even shared in the conquest(Norway for example). I believe Norway was where Hitler developed open contempt for the Russian Army and its poor offensive capabilities. Stalin also contributed to Hitlers aggression when he purged the Russian Officer Corps before WW-2. The Norweigan Military openly showed the world that the Russian Bear was toothless. It would take many years, of combat, for the Russian Officer Corps to gain the knowledge and experience to mount successful offensive operations. Hitler considered Russia to be the main obstacle to his own expansion in Europe. He didn't count on the Russian infantrymans tenacity, reckless courage, and ability to withstand hardship.