When Karl Marx and Friedrich Engels wrote The Communist Manifesto, the process of industrialisation was well-advanced in many European countries. This process transformed the economy, giving rise to increased manufacture and the factory system. It had social effects too: poverty and deprivation blighted the lives of many members of the industrial working classes. 

Against this backdrop, then, Marx and Engels argued that industrialisation had a huge impact on the proletariat. The bourgeois created "enormous cities" and thus increased the urban population. They centralised and improved the means of production, so that the proletariat were forced to sell their labour in order to survive. Inside these factories, where the proletariat sell their labour, they are organised like "soldiers" and "placed under the command of a perfect hierarchy of officers and sergeants." Women and children are not exempt from this way of life, say Marx and Engels: "All are instruments of labour, more or less expensive to use, according to their age and sex." At the end of the working week, the proletariat are paid in cash and this is then given to other members of the proletariat: the landlords, shopkeepers and tradesmen, who are all reduced to poverty because they are forced to compete with each other under the system of Capitalism. 

But the proletariat face a real problem. These wages barely pay enough to live and the work in factories is boring and repetitive. Marx and Engels believed that, over time, the proletariat would become so fed up with this situation that they would rise up against the bourgeois and overthrow society.

In summary, Marx and Engels believed that industrialisation forced the proletariat into a subservient and exploitative relationship that would eventually lead to revolution.