Romanticism was a movement in art and culture in the late 1700s and 1800s that emphasized feeling, intuition, and imagination. It was a reaction to the Enlightenment emphasis on reason (the "Age of Reason"), as well as the cold, impersonal direction of the Industrial Revolution.
If the Scientific Revolution of the 1600's had made the world seem to be a mechanical, unfeeling place, the Romantics felt their way to something deeper and more mysterious about human life. If God had seemed more distant and less certain by reason, they recognized the possession of the artist by a higher power. If Kant had suggested we cannot know the world as it actually is, they responded that they could access the world as it really is through intuition. If the Renaissance and Enlightenment had reached back to the classical world of the Greeks and Romans for examples, the Romantics reached back into the Middle Ages for shadowy tales of Arthur, Robin Hood, and the stories of the Brothers Grimm.
No doubt the popularity and influence of Romanticism derived from the fact that the common person could identify with it. It certainly had its elite leadership, individuals like Johann Wolfgang von Goethe (1749-1832) in Germany and Samuel Taylor Coleridge (1772-1834) in England (although Goethe denied that he was a Romantic). But the staying power came from the fact that anyone could identify with its values and themes. Paintings were less and less about representing truths--less about Jesus, Mary, biblical scenes. Now they were expressions of feeling and imagination, ranging from scenes of everyday life to less than reverential treatments of religious themes.
Romanticism was thus an expression of cultural insecurity, a kind of escape from the "real world" to some other supposedly more real world. It is no surprise that fear was one of the primary emotions expressed, and the modern horror film finds its origins in the Romantic Age. This is the age that gave birth to Mary Shelley's Frankenstein (1818). The movement that birthed it in Germany was called Sturm und Drang ("storm and stress"). In Goethe's Faust, a genius has studied everything imaginable ("unfortunately theology as well") and at the end of reason sells his soul to Satan.
Individualism in its modern form owes much to the Romantic Age. It is true that Descartes turned the lens of philosophy toward me as an individual thinker, but Romanticism glorified individual feeling. It was the age of the French and American Revolutions, where any individual could disregard the time honored roles and rules of society (this is part of the reason Shakespeare emerged as a hero). "Who am I and what do I feel about who I am?" became a question the elite now asked, while common
people now felt empowered and embraced a common identity as a people (nationalism). These developments would set the stage for Freudian introspection at the end of the 1800’s.