President Obama has signed legislation that, by striking a single word from longstanding U.S. nuclear defense policy, could heighten tensions with Russia and China and launch the country on an expensive effort to build space-based defense systems. The National Defense Authorization Act, a year-end policy bill encompassing virtually every aspect of the U.S. military, contained two provisions with potentially momentous consequences.

One struck the word "limited" from language describing the mission of the country's homeland missile defense system. The system is designed to thwart a small-scale attack by a non-superpower such as North Korea or Iran. A related provision calls for the Pentagon to start "research, development, test and evaluation" of space-based systems for missile defense. Together, the provisions signal that the U.S. will seek to use advanced technology to defeat both small-scale and large-scale nuclear attacks. That could unsettle the decades-old balance of power among the major nuclear states.

[...] Rep. Trent Franks (R-Ariz.), who introduced and shepherded the policy changes in the House, said he drew inspiration from President Reagan's Strategic Defense Initiative of the 1980s, which was intended to use lasers and other space-based weaponry to render nuclear weapons "impotent and obsolete." Known as "Star Wars," the initiative cost taxpayers $30 billion, but no system was ever deployed.