The Nano machines are a reality that is quite dangerous to humanity because these micro robotics can become potentially fatal and A.I is quite evolved even at this level. These are not inventions of the human race but of alien life forms who wanted to take over the planet by turning humans into slaves with Nano technology. This is the main reason why we had to eradicate them from the planet and make sure that they will not be brought back in.
The problem is that humans already tapped into the first steps of Nano technology and hopefully they will not discover their full potential at this stage of their evolution. If they do then the 3rd world war will be the last. We believe that nuclear power and Nano Technology are the biggest threats right now, but nuclear power is fully available in many countries and this makes it even more dangerous at the moment.