Printing made information available to a larger audience. It helped the development of vernacular languages, aided the Protestant Reformation, and contributed to the spread and accumulation of knowledge.
The telegraph and telephone were the first media to use electricity to communicate. They marked the first time the message could be separated from the messenger. The telegraph helped the railroads move west and permitted the newspapers to publish more timely news. The telephone linked people together in the first instance of a communication network.
Photography provided a way to preserve history, had an impact on art, and brought better visuals to newspapers and magazines. Motion pictures helped socialize a generation of immigrants and became an important part of American culture.
Radio and TV broadcasting brought news and entertainment into the home, transformed leisure time, and pioneered a new, immediate kind of reporting. Television has an impact on free time, politics, socialization, culture, and many other areas as well.
The digital revolution changed the way information was stored and transmitted and made e-commerce possible.
Mobile media have changed American culture and taken over some of the functions of mass media.
The next communication milestone is the expanding use of social media.
In general, it is difficult to predict the ultimate shape of a new medium. New media change but do not replace older media. The pace of media inventions has accelerated in recent years.
