The most accurate response is:
They learned from their mistakes in the Treaty of Versailles.
After World War I, the harsh penalties and reparations imposed on Germany led to economic distress and instability, which contributed to the rise of Adolf Hitler and the Nazi regime. After World War II, the Allies sought to ensure that Germany was rebuilt and transformed in a way that would prevent future warfare and promote stability in Europe. This involved a more comprehensive approach to occupation and reconstruction, rather than simply punitive measures.