One period of history that affirms the topic is the Colonial Period in America. The writings and actions of such as Thomas Paine, Patrick Henry, and Thomas Jefferson certainly attest to the courage and integrity that men exemplify in times of conflict. So, if the essay needs actual events as support, "Crisis No.1" by Paine, "Speech to the Virginia Convention" by Patrick Henry, and, of course "The Autobiography and Declaration of Independence" by Thomas Jefferson are excellent sources of illustration of fortitude and unexpected qualities arising from crisis and conflict.
Of course, many autobiographies also provide support for such as essay. Those of such inspiring people as Helen Keller and Richard Wright, who overcame obstacles to achieve their goals can provide the requisite support needed for such a topic.
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There are many approaches for a topic of this magnitude. If you are being asked to write this after reading a specific work of literature, I would suggest making reference to it as you compose your thoughts on how the best of individuals are evoked through conflict. Works such as Dickens' A Tale of Two Cities or Hemingway's The Sun Also Rises are but two of many literary examples that depict characters who rise to the occasion and surpass what is expected of them through situation that present conflict in its highest form. At the same time, you can use literature to show how conflict can reveal some of the negative aspects of an individual. Reading Wiesel's work, Night, as well Fitzgerald's The Great Gatsby would be examples where one can see the lesser "angels of human nature" take over during conflict situations. If you have literature of your own that has provided the base for this essay, I would use the characters depicted in helping you carve out your essay. As you make your case as to how individuals showcase their best or worst qualities when conflict is present, I would pay attention to news events and stories that might help make your case. We can see plenty of examples where individuals demonstrate their best and worst in human nature through conflict. Those who fight on the war fronts, or act in a selfless way when conflict is thrust upon them, or within individuals who battle long odds to find success. In the President's address to school children on Tuesday, he will be making reference to specific individuals who had been placed in the midst of overwhelming conflict, yet used the moment to reveal the best of their personal qualities to endure and triumph over adversity. At the same time, anytime we hear of a hero fall from grace, or of corruption and violations of the public trust, these are situations where conflict has revealed some negative and unexpected qualities of an individual. Finally, if deemed acceptable by your teacher, I would draw from personal experience to examine how your own sense of narrative has responded to the notion of conflict revealing unexpected qualities in your own life.