The Treaty of Versailles that ended WW I led to German loss of territory, restrictions on military size, and huge reparations that the German government could not afford.

Hitler achieved leadership of Germany in 1933, abolished democracy, and began a rearming campaign.

The Franco-Prussian War, the First World War and the disastrous handling of 'peace' talks in 1918 and thereafter.

The Key reason is Hitler's agression and annexation of states like austria denmark switzerland czech and foremost reason is the attack and invasion of poland by Germany. Great Britain, France and Russia Opposesd germany occupation over poland and asked them to retreat. But Adolf Hitler refused to do and the allies declared a war on germany! INTIALLY GERMANY AND AXIS

The Key reason is Hitler's agression and annexation of states like austria denmark switzerland czech and foremost reason is the attack and invasion of poland by Germany. Great Britain, France and Russia Opposesd germany occupation over poland and asked them to retreat. But Adolf Hitler refused to do and the allies declared a war on germany! INTIALLY GERMANY AND AXIS power were on the verge of victory. but the russian invasion by germany changed the course of the war.more than 1 lakh german soldiers died in the bitter cold since the russian used the scorched earth policy. it was a great loss for the german side. If russian invasion had had not happend the axis power would have won the world war II and things would have changed!