That’s an easy one for a postmodern wannabe like myself. Modernism’s grace and curse is the supremacy of the individual. Into the 20th Century we started into what many call hyperindividualism. That’s what most postmoderns are rebelling against. There was still an importance of the collective and community in 18th century, even with the rise of the rugged individual.
20th Century modernism created the individual genius. Look at what was rewarded such as with the MacArthur grants formerly known as the genius grants.
Systems and individuals became more important than the communities. We are facing a broad rebellion to many 20th Century systems in art, news, government, religion, media distribution, a decentralizing of power from previously accepted centers of power, for good or ill.