The twentieth century witnessed the greatest changes in technology and science that humans have ever witnessed. These occurred rapidly and affected such a broad range of people. Scientists, inventors, and engineers built upon the great inventions of the 19th century to expand the reach of modern technology - for a citizen in 1900, communication, transportation, and agricultural was still primarily local activities; by 2000, an American citizen was part of an interconnected global community. These developments in science and technology were also important in the social and cultural changes of the period. The Great Depression, the World Wars and Cold War, the civil rights and women's rights movements - all were greatly impacted by the rapid scientific and technological advancements in the universities and industry.