History of the Internet Part 2
Written by Eric Girouard for my internet research class at John Abbott College

In 1957, the Soviet Union launched Sputnik. As a response to the Soviet research efforts, president Dwight D. Eisenhower instructed the Department of Defense to establish the Advanced Research Projects Agency or ARPA. The agency started with great success and launched the first American satellite within 18 months of the agency's conception. Several years later, ARPA was also given the task of developing a reliable communications network, specifically for use by computers. The primary motivation for this was to have a network of decentralized military computers connected in such way that in the case of destruction of one or several nodes in a potential war, the network would still survive with communication lines between remaining nodes.

From: http://ei.cs.vt.edu/~wwwbtb/book/chap1/index.html