Buddha was a great teacher, he taught about love and happiness. For Buddha, the path to happiness starts from an understanding of the root causes of suffering. He said that inner peace happens when you understand what takes it away.
In the film "The Karate Kid" countless lessons are taught on inner peace and spiritual growth. Like "A Separate Peace" the protagonist is experiencing adolescence and the problems that come with it.
In the beginning of the movie Kung Fu Panda Po is insecure, but when master shifu teaches him about inner peace and how to be happy being himself everything changes. He becomes more confident and becomes a warrior.
Martin Luther King Jr. was fighting a war against injustice in America. The cause he was fighting for seemed impossible in the beginning, but because of his inner peace and confidence he could see what others couldn't.
In the novel "A Separate Peace" The battle for inner peace is shown throughout. Gene battles with himself as he transitions into adulthood. It is only found at the end after Finny dies, which is ironic because Finny had inner peace the whole time.
Inner peace is key.