The Gray Lady has the most comprehensive explanation that I’ve seen yet about what caused the blackout. It’s (thankfully) pretty much politics free.

Summary: it was caused by failure of not only power lines, but of the devices that warn of failure of power lines.

This is utterly unsurprising, because with a mature technology (which, after more than a century, electrical generation and distribution assuredly is), you’ll almost never get a major failure from an isolated event. It requires a(n unlikely) combination of failures, which is why it happens relatively rarely (the last time anything remotely like this happened was over a quarter of a century ago–the fact that this one was the biggest in history can be accounted for simply by the fact that we’ve grown a lot in many ways since then, and the system is more interconnected).

Examples of this can be seen in any random perusal of aviation or diving magazines, in which accidents are described in detail, and they are invariably a result of a combination of things going wrong, rather than a single one.

Consider the Titanic. Just one thing going right (e.g., seeing the iceberg in time; not using a little-understood new steel that became embrittled by the temperatures of the North Atlantic in springtime; the captain understanding that he had to have forward power to have adequate steering control, which was not possible because he decided to reverse engines at the same time he was trying to steer away; other ships being close enough, or the California receiving and understanding the radio messages; having enough lifeboats; going at a safe speed rather than trying to beat a record, etc.) and they would have been fine. But everything went wrong, and hundreds of people died.

Or the Donner Party. If there hadn’t been an early winter, or they hadn’t decided to take the “short cut,” or…many other bad decisions had been avoided, they would have been safe in California before winter hit, as their traveling companions were.

Or Challenger. If the weather hadn’t been quite so cold, if they’d understood the o-ring issue earlier, if they’d not been delayed by the previous delay caused by the desire to fly the Congressman, if only…

Or Columbia. If they’d been going to space station, if they’d not changed the insulation on the tanks for environmental reasons, if…if…if…

As I said, rarely does a single thing going wrong cause disaster. It’s almost always a combination of things going wrong, and this article just presents one more example of that.