The progress of liberty is a powerful trend. Yet, we also know that liberty, if not defended, can be lost. The success of freedom is not determined by some dialectic of history. By definition, the success of freedom rests upon the choices and the courage of free peoples, and upon their willingness to sacrifice. In the trenches of World War I, through a two-front war in the 1940s, the difficult battles of Korea and Vietnam, and in missions of rescue and liberation on nearly every continent, Americans have amply displayed our willingness to sacrifice for liberty.