EMP (Electromagnetic Pulses) will be the ultimate way that humans will become extinct. It will create a butterfly effect and that will be the end of us all. EMP warfare takes out electrity and electronics. Remember the Matrix?
Peter Pry, director of a bipartisan congressional commission called the EMP Task force said:"nine out of ten Americans could die from starvation, disease, and societal collapse if the blackout lasted a year." Just imagine this on a global scale?
It is easy to see why also. Think of everyone in hospitals, who are hooked up to machines. Anyone who takes medication to live would one day run out. Equipment that uses a computer chip operate will no longer run. No microwaves, fridges or freezers. That means no more food.
This is a great article that Vice put out
https://www.vice.com/en_us/article/we-asked-a-military-expert-how-scared-the-us-should-be-of-an-emp-attack-508
This is a good book series about an EMP attack by John Matheson
https://www.amazon.com/Second-After-John-Matherson-Novel/dp/0765356864
Really this would be a quick death for some and a slow death for others.