The correct answer is: "economic crisis and the punishment of WWI defeated powers, specially Germany"
After WWI, the Treaty of Versailles was signed in 1919, through which (among other provisions), the victorious powers: France, UK and Russia blamed Germany for all the losses suffered and imposed the dismantling of its army and the payment of very abussive war reparations.
These reparations not only exhausted the possibilities of recovery of the German economy, but also generated a feeling of nationalism against the European powers that were oppressing them. The very complicated economic situation, which led to an hyperinflation crisis, help to gain support for the extreme-right wing nationalist party leaded by Adolf Hitler, which promised to restore German pride and to recover its ancient glory.
