American exceptionalism in the twentieth century is the subject of analysis in this chapter. It notes that the early period of the century was known as the Progressive Era in which the United States went through rapid industrialization driven by scientific and technological advances. The period saw movement of people from rural to urban parts of America and immigration contributed to significant changes in society. Economic reforms were introduced and new government institutions were established to promote businesses. Industries were set up such as Ford Motor Company, which introduced the first affordable car (Model T) in 1908. The rest of the twentieth century was a period of major conflicts. In World War I and World War II, America’s entry was decisive in defeating Germany. The atomic bombing of Hiroshima and Nagasaki in Japan brought a devastating end to World War II in the Far East, and thus began the nuclear age. In the Cold War, the United States prevailed in the race for global military, economic, and ideological dominance. Finally, the Soviet state was dissolved. These and other twentieth-century events are analyzed in the chapter.