The Internet has a fascinating history, if such things interest you. There is no particular reason why you should be interested in such things, of course, except that a superficial understanding of how the Internet got started may help you to understand and cope with the way this massive computer network exists today.
The Internet traces its beginnings back to a small network called ARPANET, built by the Department of Defense in 1969 to link defense installations. ARPANET soon expanded to include not only defense installations, but universities as well. In the 1970s, ARPANET was split into two networks, one for military use (which was renamed MILNET) and the original ARPANET for nonmilitary use. The two networks were connected by a networking link called IP, the Internet protocol - so called because it allowed communication between two networks.
The good folks who designed IP had the foresight to realize that soon, more than two networks would want to be connected. In fact, they left room for tens of thousands of networks to join the game, which is a good thing because it was not long before the Internet began to take off.
By the mid-1980s, ARPANET was beginning to reach the limits of what it could do. Enter the National Science Foundation (NSF), which set up a nationwide network designed to provide access to huge supercomputers, those monolithic computers used to discover new prime numbers and calculate the orbits of distant galaxies. The supercomputers were never put to much use, but the network that was put together to support the supercomputers, called NSFNET, was used. In fact, NSFNET replaced ARPANET as the new backbone for the Internet.
Then, out of the blue, it seemed as if the whole world became interested in the Internet. Stories about it appeared in Time and Newsweek. Any company that had "dot com" in its name practically doubled in value every month. Al Gore claimed he invented it. The Net began to grow so fast that even NSFNET could not keep up, so private commercial networks got into the game. The size of the Internet nearly doubled every year for most of the 1990s. Then, in the first few years of the millennium, the growth rate slowed a bit. However, the Internet still seems to be growing at the phenomenal rate of about 30 to 50 percent per year, and who knows how long this dizzying rate of growth will continue.