A real concern - Electromagnetic Pulse

Also known as EMP - from the Washington Examiner:

China develops weapons to fry US electric grid, eyes high-tech ‘Pearl Harbor’ attack
With the help of stolen U.S. technology, China has developed at least three types of high-tech weapons to attack the electric grid and key technologies in a “surprise Pearl Harbor” assault that could send America into a deadly blackout, according to a new analysis.

According to the report from the independent EMP Task Force on National and Homeland Security, China has built a network of satellites, high-speed missiles, and “super-electromagnetic pulse” weapons that could melt down the U.S. electric network, fry critical communications, and stifle aircraft carrier groups.

EMP is a serious concern. The sun outputs strong solar flares from time to time which have the same effect. We dodged a bullet in 2012 when huge one happened but it was pointed away from Earth at the time. Nine days earlier, things would have been quite a bit different. There was a big one in 1859 - The Carrington Event and we have had other lesser storms in 1921, 1960 and 1989. These events are not uncommon.

What China is trying to do is launch nuclear weapons into orbit (and I am sure we have some up there as well) and detonate them 200+ miles up over the US. The resultant EMP would fry out power grid and kill most modern electronics.