During World War 2, American industries expanded to meet the demands of the war. This led to increased demand for Iron, Steel, Coal and Oil. This in turn created employment - brought millions of women into workforce. So, Family earnings increased. During War people had few goods to spend their income on. By 1945 Americans had $140 billion in private savings. This savings were spend on consumer goods. This led to increased consumer productions - more employment etc. With more people working, the government collected more tax.
After World War 2, the USA was the greatest economic power on the planet. By 1950 the US produced 50% of the world's manufactured goods and created 40% of the world's income.
Europe focusing on Germany
The Second World War had brought colossal destruction to Europe. Every participating country was economically exhausted after the war. Especially , Germany was a defeated nation ,so hit the hardest. The first several years post World war 2 were bitter penury for the Germans. Seven million forced laborers left for their own land, but about 14 million Germans came in from the East. It took nearly a decade for all the German POWs to return. High inflation made savings lose 99% of their value, while the black market distorted the economy.