Farming

 Changes in agriculture 1900-1950

https://livinghistoryfarm.org/farminginthe50s/life_11.html

https://eh.net/encyclopedia/u-s-agriculture-in-the-twentieth-century/

https://www.quora.com/What-is-the-percentage-of-people-in-the-US-that-worked-in-agriculture-in-the-1800s

https://eh.net/database/u-s-agricultural-workforce1800-1900/

http://www.pbs.org/ktca/farmhouses/sustainable_future.html

http://jaysonlusk.com/blog/2016/6/26/the-evolution-of-american-agriculture