The correct answer is - Nationalism.
Both Italy and Germany were countries were the people lived in terrible conditions. The moral was low. The unity was almost non-existent. The economies were in bad conditions.
Hitler and Mussolini used all of this things, and presented their ideology to the people as a unifying one. They promoted socialism, but also nationalism, and used the nationalism to make the people feel like a part of something big and united, feel special, distinct, and worthy of greater things.
Unfortunately, they also promoted hatred towards other nations, and also inferiority of the other ethnic group.