TigerHawk asks:

So, if an existential war against Islamo-fascism is as inevitable as World War II became after the appeasement of the 1930s, what event would be necessary to motivate the United States to militarize its society and economy to fight that war? What event, if any, would militarize Western Europe?

This is strictly off the top of my head, so take it with a grain of salt. But here's my very initial take.

If 9/11 didn't cause President Bush to militarize America's society and economy, I can only assume that it would take, God forbid, a nuclear blast, or the successful completion of something on the order of what the terrorists captured this past week had planned. But even then, as we've seen with our efforts in Iraq, it would only be a matter of time before the elite media and the left (sorry to be redundant) began to second-guess any military efforts, and undermine them.

As for continential Europe, forget it. I concur with Jonah Goldberg's assessment of the extent that the level of America's Cold War-era protection of western Europe has allowed their collective welfare states to grow so large that they've sapped their countries' armies:

By taking their defense for granted for so long, too many of our allies believe that talk can get them everything they need. Like the kid living off his Chevron card, they've come to believe the world is like a giant college campus, where conflicts may erupt in the form of debates and shouting matches but violence is simply "against the rules," and where being asked to pay your own way in the world seems an absurd injustice.

And as Mark Steyn wrote in 2004:

For more than a week now, American friends have asked me why 3/11 wasn't 9/11. I think it comes down to those two words you find on Holocaust memorials all over Europe: "Never again." Fine-sounding, but claptrap. The never-again scenario comes round again every year. This very minute in North Korea there are entire families interned in concentration camps. Concentration camps with gas chambers. Think Kim Jong-Il's worried that the civilised world might mean something by those two words? Ha-ha.

How did a pledge to the memory of the dead decay into hollow moral preening? When an American Jew stands at the gates of a former concentration camp and sees the inscription "Never again", he assumes it's a commitment never again to tolerate genocide. Alain Finkielkraut, a French thinker, says that those two words to a European mean this: never again the führers and duces who enabled such genocide. "Never again power politics. Never again nationalism. Never again Auschwitz" - a slightly different set of priorities. And over the years a revulsion against any kind of "power politics" has come to trump whatever revulsion post-Auschwitz Europe might feel about mass murder.

That's why the EU let hundreds of thousands of Bosnians and Croats die on its borders until the Americans were permitted to step in. That's why the fact that thousands of Iraqis are no longer being murdered by their government is trivial when weighed against the use of Anglo-American military force required to effect their freedom. "Never again" has evolved to mean precisely the kind of passivity that enabled the Holocaust first time round. "Neville again" would be a better slogan.

So the real question is, what will it take to militarize the allies in the Anglosphere we already have: Britain and Australia? (Canada's new prime minister might be willing to join in, but I suspect after decades of Trudeaupia, its military is probably about the shape that most of Old Europe's is in.)

As I said, an absolutely horrific attack might do it--but possibly not even that.