In 1969, when few commercial communications networks existed, a U.S. Defense Department research agency created an experimental system that would eventually become the Internet. Driven by both research and military considerations, the designers of the Internet created a complex, robust, and flexible system that differed in significant ways from contemporary commercial communications networks. In the 1970s and 1980s, computer manufacturers (mainly based in the United States) and telecommunications carriers (mainly operating outside the United States) vied to offer commercial network products and services, but no single company or technology was able to dominate the market, in part because computer users preferred the type of nonproprietary technical standards used in the Internet. In the 1980s, the National Science Foundation took over operation of the Internet, and in the 1990s the NSF turned over the network to privatesector operators. While the Internet has rapidly increased in scale under commercial ownership, the technology also continues to reflect the systems research origins.