The latter kinds of ideas are those which are the concern of this book. In its pages we have attempted to demonstrate how ideas with a purpose, spread by men with missions, have in?uenced the destinies of nations and the lives of individuals throughout history and at the present instant. If this book has a moral, it is the simple fact that the most important things each of us possesses, the freedom of our minds and spirits — in short, the things that make life worth living — are at the mercy of the force of such ideas and of men with such missions.