Which major event resulted in the government taking on a much larger role in social policy, including the creation of social security?

Great Depression

Explanation:

The Great Depression of the 1930s was the largest recession in history and its causes were overproduction of goods and the expansion of unbridled credit by banks. The American economy was experiencing a period of euphoria during the 1920s. The US had become the world's leading economic powerhouse and was the largest supplier of manufactures to Europe. In this scenario, banks have expanded their credit rampantly to sustain the increase in production. However, production increased in a way that there was not enough consumer market to dispose of the products. The businessmen lost the conditions to pay their loans to the banks and the financial system collapsed.

The Great Depression was overcome from President Roosevelt's New Deal plan. One of the main concerns of the New Deal was the plight of the people. It was in the context of the New Deal that the main social achievements of the country emerged, especially the social security that guarantees income to the elderly.