Answer:
The Great Depression.
Step-by-step explanation:
The Great Depression of 1929 was a major economic depression that started in the United States and spread around the whole world. The sudden crash of US stock prices on October 24, 1929, is usually considered the event that triggered the Great Depression. The severe decline of the US economy as a consequence of the stock market crash had a ripple effect that stretched across the planet, sinking most capitalist economies into economic depression.
According to the then dominant economic theory, the state had virtually no role in the economy, other than protecting private property. Market forces would, through the invisible hand of the market, naturally find a healthy balance. However, after the Great Depression, economists such as John Maynard Keynes argued that the state had to play a major role in the economy, mostly by investing massively during economic slowdowns to compensate for the lack of private investment. Keynes argued that keeping people employed and working would eventually create the demand needed to reactivate the economy. Soon, most capitalist economies adopted some sort of Keynesian state intervention policies to lift their economies out of the slump of the Great Depression. Keynesian economics and the resultant mixed market economies would remain the mainstream in economics until the 1970s.