Which era is characterized by things such as artists struggling against the conventions of society, the creation of music that unsettles rather than soothes, and the focus on artistic and musical individualism?

This seem to be Modernism.

Explanation:Struggling with conventions with society is reflected in the modernist view that traditional beliefs, philosophy, science and art are ill-fitted to their tasks being not in line with real environment. As for music, the unsettling character might be explained by the fact that Modernism in music had a tendency to reflect social disorder,decline of civilization and its transformation to cold machinery and capitalism. And finally, individualism is another characteristic of Modernism since it is focused on self-conciousness and belief of the person to reshape,reform and improve the environment.

12-bar blues chorus = a a b