2

At the end of the book, Joe realizes that he is the future. By that, he means wars and the outcome of wars are the future. He believes that once people see him, they will see how horrible war is and would never want to fight again, and that could possibly prevent the horrible future that Joe believes in.
He is pointing the gun at the people with the power because all they do is just to declare war against countries and send troops to fight for the country, however they never do