The proliferation of drone technology has moved well beyond the control of the United States government and its closest allies. The aircraft are too easy to obtain, with barriers to entry on the production side crumbling too quickly to place limits on the spread of a technology that promises to transform warfare on a global scale. Already, more than 75 countries have remote piloted aircraft. More than 50 nations are building a total of nearly a thousand types. At its last display at a trade show in Beijing, China showed off 25 different unmanned aerial vehicles. Not toys or models, but real flying machines.