If the Enlightenment was a movement which started among a tiny elite and slowly spread to make its influence felt throughout society, Romanticism was more widespread both in its origins and influence. No other intellectual/artistic movement has had comparable variety, reach, and staying power since the end of the Middle Ages.
Beginning in Germany and England in the 1770s, by the 1820s it had swept through Europe, conquering at last even its most stubborn foe, the French. It traveled quickly to the Western Hemisphere, and in its musical form has triumphed around the globe, so that from London to Boston to Mexico City to Tokyo to Vladivostok to Oslo, the most popular orchestral music in the world is that of the romantic era. After almost a century of being attacked by the academic and professional world of Western formal concert music, the style has reasserted itself as neoromanticism in the concert halls. When John Williams created the sound of the future in Star Wars, it was the sound of 19th-century Romanticism--still the most popular style for epic film soundtracks.
Beginning in the last decades of the 18th century, it transformed poetry, the novel, drama, painting, sculpture, all forms of concert music (especially opera), and ballet. It was deeply connected with the politics of the time, echoing people's fears, hopes, and aspirations. It was the voice of revolution at the beginning of the 19th century and the voice of the Establishment at the end of it.
This last shift was the result of the triumph of the class which invented, fostered, and adopted as its own the romantic movement: the bourgeoisie. To understand why this should have been so, we need to look more closely at the nature of the style and its origins.
Origins:
Folklore and Popular Art
Some of the earliest stirrings of the Romantic movement are conventionally traced back to the mid-18th-century interest in folklore which arose in Germany--with Jakob and Wilhelm Grimm collecting popular fairy tales and other scholars like Johann Gottfried von Herder studying folk songs--and in England with Joseph Addison and Richard Steele treating old ballads as if they were high poetry. These activities set the tone for one aspect of Romanticism: the belief that products of the uncultivated popular imagination could equal or even surpass those of the educated court poets and composers who had previously monopolized the attentions of scholars and connoisseurs.