What is the greatest influence on the course of human history, its social and cultural development? Some say it’s powerful ideas like socialism, democracy, human dignity, and scientific method. Some say it’s the social movements that embody and promote these ideas. But the greatest influences are wrought by great leaders, who are not necessarily great thinkers. Throughout history, every time a great leader appeared— Moses, Alexander, Caesar, Napoleon, and the like—the world was irrevocably changed regardless of what ideas or social movements were in existence.