Diesel generators are what keep most third world cities intermittently lit at night.
Start of a trend? Massive influx of seventh century savages followed by decline in civil behavior and rule of law.
Just need machete-armed gangs to make it real.
Not just the third world.
The island of Kauai in Hawaii is powered by diesel generators. They have some alternative energy, but not enough to even make a small dent.
They bring the diesel by barge to Port Allen.