The governments of the world have no grudge against each other for each has their own problems and don't have time to deal with each other.
Let's go over to pretty average neighborhood, nothing out of the ordinary with it. You can see all the cars parked in their driveways, average sized houses. But don't let this deceive you, for a hacker, has been hacking away (Ha, get it?) to get into the government files.
The hacker cracks the code. The person clicks shut down. All the power in the U.S. goes out, only the hacker remains, then starts going to social media saying that U.S. shut down because country is targeting (social media was working for a short time). The country goes into chaos.
Everyone around the world was convinced and governments too. The world starts declaring war, blaming. Some even plan to use Hydrogen warheads, Nuclear Warheads, you name it. Some even declaring this World War III .
Back to that average neighborhood, someone was going home, avoiding being seen since people are accusing anyone they see. But then he saw the hacker was the only one with power. SInce the phone lines and internet is out, so he takes the situation into his own hands. Though I will not describe for this is being viewed in a school environment.
In the end don't let something like this make you do things that you would never do. The world found out that the U.S. was hacked and stopped fighting. The power came back to the United States, everything, was not normal, but under control.