The potential changes in the operating environment (OE) and the character of war in the next 15-20 years are unknowable and history cannot provide a predictive model or “cookbook” to anticipate future events. The last 250 years, however, have provided many examples of shifts in the character of war caused by emerging technology, political shifts, economic changes and diplomatic crises. This context may prove very useful for senior leaders. There will doubtless be technological advances in the future, and some may be “game changers.” Intellectual development is just as important as technological development. The Army learned during the interwar years between the world wars that maintaining intellectual capital was critical to later success. Technological change is constant, and all armies adapt to it, yet not all technological changes affect the character of war. The machine gun and the computer, for instance, revolutionized tactics, but had little effect beyond the battlefield. The advent of submarines, airplanes, and nuclear weapons, however, fundamentally altered how war is conducted—the character of war. These case studies address periods during which the character of war changed.