On Aug. 9, 2019, the lights went out in large parts of the UK, where 936,000 UK residents were suddenly without power. The breakdown only lasted an hour, but it happened right in the middle of rush hour, leading to commuters being trapped for hours on trains and London-bound flights being canceled, among other things.

Despite its brief duration, this blackout in the UK is regarded as the worst of its kind in a decade, and that's because it wasn't just a breakdown at a power plant or an interrupted connection.