Emergence of Realism
The beginning of the 18th century (1700 - 1800 AD) was a natural conclusion of the trends of the Renaissance. The Medieval period had held everything in lower esteem than spiritual truth, art included. The Renaissance had brought a new passion to art and a focus on naturalness and beauty, ideals which resonated with and celebrated the aristocracy and their lifestyle. This trend climaxed in 1700 with the introduction of the Rococo style, a highly ornate style which prized gaudy displays of exceptional size entirely filled with a visual explosion of minute detail which consumed even the smallest spaces of the canvas. The Rococo dominated sculpture, painting, and the crown jewel of the Rococo period, architecture. Favorite subjects included nudes, people juxtaposed with fantastic landscapes, and most popularly mythological themes. Elaborate use of gold and mirrors were juxtaposed to create stunning effects, perfectly expressing the twin obsessions of wealth and self-gratification so dear to the hearts of the Renaissance aristocracy in Europe.
After 1750 AD, everything changed. Watching European artwork of the period transform is simply breath-taking. Overnight, ornate yields to simple, airy lightness to boldness, pastels to bright colors. Favorite subjects are dominated by real world motifs: landscapes / seascapes, portraits, and historical paintings. The middle class was interested in the things which related to them. It was the artistic expression of the philosophical and soon political realities of the continent. Yet even before any of the social changes which were about to rock the continent, you can see the revolution occuring in people's minds expressed visually in the transformation of European art.
The dominance of the aristocrats was waning; in the next 50 years, both the American and then the French Revolution would violently overturn monarchies and put power in the hands of the people (though the revolutions diverged radically from there). A booming new business in art catering to the middle class emerged first in the wealthy Netherlands from whence it spread across Europe. Here at least, late Song China does give us some corroboration; the arts patronized by the middle class were emerging as important new trends in Chinese culture before it fell to the Mongols. Economic power was a driving force in the expanding power of the middle class, and it was transforming both philosophy and the arts in China.
The variety of Industrial Era art was unique as well. The aristocratic or monarchical elite were frequently a closed, relatively homogenous group throughout history; on the other hand, the middle class was a stunningly diverse group and the art they liked was equally diverse. Thus, the dominant realism shared the spotlight with the related movement towards rationalism, the belief that truth made logical "sense". This was very similar to, even modeled on, the ideas of Aristotle, so there's no surprise that rationalists supported an alternative school of art called Neoclassical. Classical subjects were dominant (though primarily historical, not mythological) and demonstrated a minimalist, very clean, bright style.
Naturally, the twin schools of realism and rationalism were linked by their emphasis on cold dry facts whether the "natural science" of the realists or the intellectual abstractions of the rationalists. It was therefore only a matter of time before an artistic reaction emerged championing emotion and human intuition over logic; thus romanticism was born. Moreover, the artists of each school – especially the realists and romantics – expressed a diversity of viewpoints and a depth of individuality which had rarely been seen in previous schools of art. The abundance and creativity of Industrial Era art demonstrates the vitality and breadth of the interests of the middle class as they emerged from the shadows of the aristocrats.