Basically there was a deluge of people who moved to the cities to work in the factories, before the Industrial Revolution, during the Medievel Age, most of Europeans lived by subsistence agriculture and in Ancient times, Greeks and Romans for instance could have more urban lives due to the slave support they had.
For the first time in History there was this massive exodus to cities and thanks to Industrialization, new technology increased exponentially, as technology built over technology. With everything Industralization brought about it is possible to say that a middle to lower class worker today has a better, more comfortable life than kings and queens had in the Medievel Age.