American military leaders have warned that nations are developing advanced missile technologies that outpace existing U.S. defenses.

General Stephen Whiting tells Chicago forum that Beijing has spent three decades preparing to target US infrastructure.

It would be the equivalent of us going back 1,000 years and having to start from scratch." In response to these hypothetical - but experts say quite possible - threats, US President Donald Trump has set his eyes on a "next generation" missile shield: the Golden Dome.