A local short circuit may overload the system, and trip some circuit breakers. But then those breakers can be flipped back on. To really destroy a power grid,

A local short circuit may overload the system, and trip some circuit breakers. But then those breakers can be flipped back on. To really destroy a power grid, you need mother nature. I remember the great ice storm of 1998. Huge amounts of freezing rain coated transmission lines with inches of ice, and the weight toppled hundreds of pylons in the Montreal area. The metropolis and the region South were without power for weeks. And it was January. And Montreal gets brutally cold at that time of the year. Perversely, you need electricity to run a fuel oil house furnace. Some people were without it for a month. We wanted to buy a generator for my mother in law, who lived South of Montreal. We lived in New Jersey. We went to the local home depot and bought the last one. The people behind us in line at the store were from Montreal. There were no generators left in the stores from Montreal to new Jersey. See "January 1998 North American ice storm"