Most amount of damage/money lost from single civilian act?

I might be wrong in that crocodiles were worshiped for tens of thousands of years before any man (or personified god.)

…your point being?

It’s not so much which is more dangerous at status quo but more with the level of change it implies and how much more resistance and conflict it will cause.

HUH?!? In what bizzaro-world scenario can you possibly imagine us having invaded Iraq if 9/11 hadn’t happened? And please don’t say ‘to avenge the plot on his dad’…

The Project for the New American Century, which included Cheney, Rumsfeld and Wolfowitz, was advocating action against Iraq beginning in the late '90s.

Regime change in Iraq became an official US policy goal under Clinton.

The removal of Saddam Hussein was a top agenda item for the new Bush administration in January 2001.

There were periodic air strikes on Iraq throughout 2001.

Immediately following 9/11, Bush sought “any shred” of evidence that Iraq could be “linked in any way.”

Yes. Although “Gavrilo Princip” is a provocative and interesting answer, Europe in 1914 was “pregnant with war,” in John Keegan’s memorable phrase. Nations were armed to the teeth with huge mass armies, much larger than any that had come before, and the new railroad systems promised to deliver them rapidly against any adversary. Meanwhile, Europe was still plagued by the old imperialist morality, in which nations threatened and used war to acquire territory or even small momentary advantages. People were used to much more limited wars, conducted with an eye to the balance of power, in which small armies fought short campaigns before one government or the other conceded and a treaty was struck, limiting the change in the status quo.

Heavily armed, flush with booming populations, and well-financed (in comparison to their previous scrambles for revenue), Europe’s confident, truculent leaders were looking to expand, limit their neighbors’ expansion, or settle old scores – unaware of the terrible synergies lurking in the combination of modern rapid-fire weaponry, mass armies, and commitment to total war.

To put it bluntly – since Iraq didn’t have anything to do with 9/11, and that was mostly clear at the time and entirely clear in hindsight, it’s reasonable to suppose the US invasion of Iraq also had nothing to do with 9/11. From there it’s a small jump to presume it could have occurred in a world where 9/11 didn’t.

You can’t really put a dollar amount on this, but an arsonist named Herostratus burned down the Temple of Artemis on July 21, 356 BC. Incinerating a wonder of the world for a bit of infamy is a pretty dickish move.

Just remembered another one: James Scott, who intentionally destroyed part of a levee so the flood waters would keep his wife stranded while he partied it up (doesn’t get much more moronic than this). Again, no dollar estimate on the damages, but the breach flooded 14,000 acres of farmland, destroyed buildings, and closed a bridge.

I considered the Chernobyl disaster, but Wikipedia describes a team of technicians at fault and the damned thing could have gone to pieces anyway in the long run.

For an alternative to oil spills from ships there’s the Halifax Explosion, 2000 odd people dead and 531 odd million Canadian dollars in damages. I think the blame might fall squarely on the captain of the cargo ship Imo, which charged through Halifax harbour and collided with a munitions vessel, igniting its cargo.

Last year’s Southwest Blackout knocked out power to 7 million people and was caused by one technician mistakenly flipping one switch. I’ve never seen a dollar amount estimate of the damage, but the lost productivity alone has to run into the hundreds of millions.

But the Bush administration would never have had the political and especially the popular support for such an invasion without the 9/11 attacks. It was a mixed bag even with it. He didn’t exactly win re-election by a landslide. Every possible ‘what-if’ scenario, policy, contingency plan is always studied, rehearsed, and kept on the back burner in every presidency, it’s just common sense. But acting on a major one like this out of the blue would have been political suicide. Not to mention impossible because neither Congress nor The U.N. would have authorized/endorsed it.

[/hijack over]

I think the OP is strictly looking for things caused literally by a single individual, and that leaves out things like war, revolution etc.

One I can think of that hasn’t been mentioned: ole Capn’ Hazelwood passing out drunk behind the wheel of a supertanker. Caused damage in the billions and was pretty much all his fault.