Philip Caputo talks about his journey across America, from the nation’s southernmost point to the northernmost point reachable by road, with an Airstream in tow. Along the way he asked Americans what unites and divides a country. In The Longest Road: Overland in Search of America, from Key West to the Arctic Ocean, he looks at how the United States, peopled by every race on earth, remain united despite all the conflicts that could cause us to pull apart.