Four years ago, about 40 million Americans and 10 million Canadians plunged into darkness as Northeastern and Midwestern US, as well as Ontario lost electrical power.
BlogTO has a "flashback" article marking the anniversary of the Great Northeast Blackout of 2003 [wiki]:
Something magical and beautiful can be seen in many people's recollections of their experiences during the blackout. It helped many people transcend usual social barriers by breaking down or simply pausing the normal framework of society. It encouraged people to take a step away from rushing from the grocery store to their home to catch a television show and instead engage with their surroundings. [...]
We witnessed people spontaneously directing traffic through intersections around there, something that I've come to realize was pretty widespread.