The roughly eight decades, beginning in Britain in the mid-18th century and spreading across northwestern Europe and North America in the 19th, in which mechanization, factory organization, fossil-fuel energy, and new forms of transport (canals, then railways) transformed what human societies could produce and how they lived. Output per person, which had drifted near-flat for millennia, began the exponential climb that continues today.
Its consequences for political thought were enormous. Adam Smith's Wealth of Nations (1776) had already theorized the division of labor; Ricardo's classical political economy tried to model the emergent system; Friedrich Engels's Condition of the Working Class in England (1845) documented its human cost in Manchester slums; and Karl Marx's Capital attempted a comprehensive critique. Classical Liberalism found its mature form defending the emerging order, Marxism its most influential shape attacking it.
The Revolution also remade the social categories through which people understood themselves. "The working class" as a self-conscious political actor is a creation of the factory system. So is "the middle class" in its modern sense. Urbanization, literacy, mass newspapers, and eventually mass politics followed in its wake. The anxieties of Romantic poets about a mechanized, de-natured life, the utilitarian reformers' battles over factory hours and child labor, and the emergence of trade unions and socialist parties all belong to this long event.
Debate continues about why Britain first: coal, institutions, empire, wages, culture, sheer accident — every answer has its advocates, and the question remains one of the most productive in economic history.