A looming threat of digital collapse. Concerns arose in the late 90's that the calendar data stored in computers wouldn't successfully switch over to the year 2000, resulting in massive computer failure across the globe.
The issue was corrected. The masses never got the apocalypse they were promised. The tension broke when the ball dropped and the year 2000 greeted the world, not with blackouts and armageddon but champagne and fireworks.
But mankind realized then the fallibility of their machine; that the system they'd built was one capable of betrayal.