Conservatives backed war in Iraq, and they’re now backing an escalation of the war in Afghanistan. Liberals (at least, dovish liberals) have warned in both cases that killing terrorists is counterproductive if in the process you create even more terrorists; the object of the game isn’t to wipe out every last Islamist radical but rather to contain the virus of Islamist radicalism.

One reason killing terrorists can spread terrorism is that various technologies — notably the Internet and increasingly pervasive video — help emotionally powerful messages reach receptive audiences. When American wars kill lots of Muslims, inevitably including some civilians, incendiary images magically find their way to the people who will be most inflamed by them…

Exhibit A in this argument is Nidal Hasan. By all accounts he was pushed over the edge by his perception of the Iraq and Afghanistan wars. He also drew inspiration from a radical imam, Anwar al-Awlaki. Notably, it had been eight years since Major Hasan actually saw Mr. Awlaki, who moved from America to Yemen after 9/11. And for most of those years the two men don’t seem to have communicated at all. But as Major Hasan got more radicalized by two American wars and God knows what else, the Internet made it easy to reconnect via e-mail.

The Fort Hood shooting, then, is an example of Islamist terrorism being spread partly by the war on terrorism — or, actually, by two wars on terrorism, in Iraq and Afghanistan. And Fort Hood is the biggest data point we have — the most lethal Islamist terrorist attack on American soil since 9/11. It’s only one piece of evidence, but it’s a salient piece, and it supports the liberal, not the conservative, war-on-terrorism paradigm.