Answer:
Before Pop Art, paintings were made of people or places. The goal was to make it very life-like and as beautiful as possible. When Pop Art emerged, it took aspects out of daily life (such as commercials, commercial products and comic books) and started painting those.
The best book about Pop-Art and its history is "Pop Art Portraits". It tells you about the history of the style, while putting it in the context of the events in the world at the time.
It practically destroyed art.