Chapter 8 provides a brief history of US air power doctrine development after World War II, along with a synopsis of the modern air wars since Vietnam. Four operational and five environmental factors that impacted air operations in Vietnam are introduced to help explain when air power is likely to be effective. These nine factors are air superiority, air-to-ground capability, friendly ground force capability, enemy ground force capability, weather, lighting, geography and terrain, civilians, and concealment and cover. A summative assessment follows, which correlates these conditional factors with the military and political outcomes for the twenty-three modern US air campaigns. Finally, nine general observations are provided as to the overall effectiveness of modern air power.