Well, what did the masses that used to be farmers do when we moved from 50% of the United States being farmers to the current levels of ~2%?
Didn't that work in the opposite way, though? New opportunities appeared that pulled (sometimes forced) people away from farming; it wasn't like there was a bunch of unemployed ex-farmers who suddenly started finding new jobs.
Which time period in history? In the 1830s, you'd get younger sons or daughters of a farming family who would move away to the city to earn extra spending money for their family and find a measure of independence; oftentimes the eldest son would inherit the farm, so there was no place there for the other children.
In the 1930s, the farms were themselves collapsing. Mechanized agriculture created both a huge oversupply of produce (which drove down prices) and also ruined the ecology of the plains, which eventually led to the dust bowl. Farmers absolutely were forced off their land: that's where we got Okies, Hobos, the Great Migration, Grapes of Wrath, and all those other subcultures of migrant workers from.
Didn't that work in the opposite way, though? New opportunities appeared that pulled (sometimes forced) people away from farming; it wasn't like there was a bunch of unemployed ex-farmers who suddenly started finding new jobs.