By 1850, the percentage of the american labor force employed in agriculture had declined to

By 1850, the percentage of the American labor force employed in agriculture had declined to 55 percent.
As America grew more advanced, most people went to big cities to work in factories and be paid more because staying in the countryside dealing with agriculture wasn't as lucrative anymore in a rising civilization. This is why the number greatly dropped.

The answer is society was a caste like system with poor whites at the bottom of the white social ladder.

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