Psychology is the science that will determine who wins and who loses the wars of the 21st century, just as physics ultimately led the United States to victory in World War II. Changes in the world's political landscape coupled with radical advances in the technology of war will greatly alter how militaries are formed, trained, and led. Leadership under fire - and the traits and skills it requires - is also changing. Grant, Lee, Pershing, Patton - these generals would not succeed in 21st century conflicts.