After WWI, the Allies made Germany sign the Treaty of Versailles, it was really harsh towards Germany, its destroyed it's economy, its army, and blamed the war on them.
Many Germans, suffering in these conditions, saw Hitler's party as a light, as hope for a better life for them an and their children, because Hitler wanted to restore Germany's glory, and with it, it's economy.
They felt betrayed by everyone, but Hitler was always on their side.