During the Industrial Revolution, companies attempted to maximize the output of their factories by keeping them running as many hours as possible, typically implementing a "sun up to sun down" workday.
Wages were also extremely low, so workers themselves often needed to work these long shifts just to get by, including often sending their children to work in the factories as well, rather than getting them educated.
With little representation, education, or options, factory workers also tended to work in horrible working conditions to go along with the bad hours.
The typical workday at this time lasted anywhere from 10 to 18 hours per day, six days a week.
This all began to change in the 19th century.
The first to suggest an eight hour workday for everyone was a British man by the name of Robert Owen, who was also one of the founders of socialism.
Owen felt that the workday should be divided into thirds, with workers getting equal time to themselves and to sleep as they did for work.
Thus, in 1817, he began campaigning for an eight-hour working days for all workers, coming up with the phrase, "Eight hours labor, eight hours recreation, eight hours rest." Unfortunately, this did not catch on for some time, though throughout the 19th century a series of Factories Acts were passed that steadily improved working conditions and reduced work hours for factory workers.
For instance, The Factories Act of 1847 stipulated that women and children were to be granted a ten-hour workday, thus only having to work 60 hours a week.
The eight-hour workday cause was taken up once again in Britain in 1884 by Tom Mann who was part of the Social Democratic Federation.