What is humanity? Humanity, to me, is the multiple aspects of human, life, mind and behavior. It involves the human mind, the way of living as a human, and the world population of humans.
Humanity is an extremely important part of literature. Every single aspect of literature out there involves humanity in some way, shape, or form. First off, most protagonists in stories are humans. The story will center on them - their way of living, their thinking, their habits, and the people in their lives. The story will usually conclude with some sort of personal outcome of theirs, or will be centered around an issue in the protagonist's life. Many stories can be based on, or during a famous historical event, with is another aspect of humanity - human living conditions years ago.
Literature more or less thrives on humanity, in my opinion - we are simply telling stories of the human mind, and the human life.