The Keynesian system of ideas is one of the most significant schools of economic thought that being used in the modern economy. The school began with the publication of Keynes's The General Theory of Employment, Interest and Money in 1936 and remains a major presence in orthodox economics today. Various aspects of the classicalist and Neoclassicalist were criticized by Keynes, yet the development of Keynesian system could not be totally independent to the two major schools of thought. For example, he lumped together with Ricardian doctrines under the heading of "classical economics," he used many of its postulates and methods. His system was based on a subjective psychological approach, and it was permeated with marginalist concepts, including static equilibrium economics. Keynes disassociated himself from attacks on the neoclassical theory of value and distribution.

Extracted from: Brue, S. L. and Grant, R. R.(2013). The Evolution of Economic Thought, 8th Edition. Cengage Learning, pp. 455

Q: Based on your understanding, explain what are the change in the economic that led to the emergence of Keynesian school of thought?