Matthew Yglesias posted an image from an infographic released by the Census Bureau showing differences in the U.S. population between 1940 and 2010. This section of the graphic focuses on changes in the industries in which the U.S. workforce is employed. For instance, in 1940 23.4% of Americans worked in manufacturing, down to 10.4% in 2010:

Education, health, and social services have emerged as a major employment sector. On the other hand, while agriculture is a minor  sector today (in terms of % of people employed), in 1940 nearly 1 in 5 people worked in agriculture. As Yglesias says,

…this drives home the fact that the initial exclusion of agricultural workers from Social Security [as part of the New Deal in the 1930s] was a really major compromise.