Final answer:
The need for labor on farms during the 20th century decreased due to technological advancements, the Industrial Revolution, and societal changes like reduced child labor and urban migration. Mechanization allowed for increased production with fewer workers, leading to a major workforce shift from rural to urban areas.
Step-by-step explanation:
The need for labor on farms during the 20th century decreased primarily due to technological advancements and efficiency improvements in agricultural production. Innovations such as the steam engine and electrical power, along with significant machinery developments, enabled farms to produce more with fewer workers. This mechanization diminished the requirement for large numbers of farm laborers and facilitated a historic shift in employment from rural to urban areas, thus altering the workforce and social landscape significantly. Moreover, the Industrial Revolution had far-reaching effects, encouraging people to migrate from farms to cities in search of factory jobs, which in turn affected family size, labor practices, and urbanization. This was compounded by societal changes such as reduced child labor due to legal reforms and a philosophical move towards education and away from widespread child work.
In the United States, the aftermath of World War I saw a significant migration from rural to urban settings because of overproduction in agriculture leading to falling commodity prices and farm foreclosures. The advent of the Industrial Revolution continued to drive urbanization across the globe, further reducing the agrarian workforce as people moved into cities for industrial job opportunities. This trend continued throughout the century and was particularly accelerated by government policies aimed at eliminating child labor and increasing industry regulations.