I'm assuming you're talking about pre-WWII with Adolf Hitler.
After WWI, the Allied Forces created a treaty called the Treaty of Versailles which heavily and brutally punished Germany, leaving them with a broken infrastructure and an extreme amount of debt. Germany was poor, riddled with falling bridges and a lack of respect across the world, this allowed Adolf Hitler to create a movement that tapped into the citizens of Germany's anger and sadness, although that doesn't really explain why they thought the Jews were responsible for everything.
Sorry, Judaism.
