What if we can’t all get along? What if it really is a cruel world?

Those questions become more relevant as we evaluate the latest terrorism news: On Tuesday, Michael Chertoff, secretary of the Department of Homeland Security, said he had a “gut feeling” that an attack might be coming. And the same day, ABC News’ Brian Ross reported that the White House had been convening emergency meetings.

Now, of course, some will dismiss all this as “wag the dog”-type fear-mongering. But surely Sept. 11 taught us that cynical complacency is no longer a good option.

Indeed, the number of terrorists has multiplied in recent years, as their origins have diversified. We might pause to consider the latest bunch of bombers to be convicted in Britain, because their terrible stories shed light on the consequences of multiculturalism, especially when it’s imported from the Muslim world.

On Monday, four men – Muktar Said Ibrahim, Ramzi Mohammed, Yassin Omar, Hussain Osman – were convicted of attempting mass murder aboard London transit on July 21, 2005. These were the “7/21” plotters, who failed, as opposed to the earlier “7/7” plotters, who homicidally succeeded. And neither group is to be confused with the most recent gang of terrorists who attempted murderous acts in London and Glasgow last month.

The ringleader was Ibrahim, born in Eritrea. That’s an African country which, according to U.S. government data, enjoys (if that’s the right word) an annual per capita gross domestic product of $700; that puts it 221st in world rankings. Despite a string of convictions for robbery and assault, Ibrahim was able to gain British citizenship, entitling him to live in a country with a per capita GDP of $27,700.

One might suppose that Ibrahim, finally ensconced in the United Kingdom, would settle back and enjoy the economic opportunities of a rich capitalist country – or at least the comforts of a well-funded welfare state. But no: Citizen Ibrahim immediately used his British passport to travel to Pakistan to take lessons in jihad. Talk about ingratitude.

And the others were no better and no more grateful to their host country. Ramzi Mohammed, born in Somalia (per capita GDP: $500), was videotaped pointing his bomb-filled backpack toward a woman with her child in a stroller, as he tried, and failed, to detonate the backpack. How many more like that do you want in your country?

The obvious point is that all the money, democracy or liberty that Britons enjoy didn’t do a thing to pacify the 7/21 plotters. As their trial demonstrated, they were all hopped up on anti-Western Islamic radicalism. And it’s obvious to even the most casual observer that such jihadism enjoys considerable quiet support among Muslim populations, not only in the United Kingdom but also in the United States. Indeed, such anger is part of a worldwide groundswell.

What makes Muslims angry? Some say it’s Israel. Some say it’s the Afghanistan and Iraq wars. Some say it’s our mere existence.

Whatever the cause of Muslim anger, our cultures don’t seem to be getting along too well. And that has implications for the future – and for our survival: First, let’s stop kidding ourselves that our bloody attempts to “liberate” them are going to turn foes into friends. If Muslims don’t like us in democratic Britain, they aren’t going to like us in a democratized Saudi Arabia.

Second, let’s build a big wall of protection, civilization-wide, against dangerous people. The goal shouldn’t be war but rather separation – which is the opposite of war. And for those already here, let’s revive old social safeguards, such as good-citizenship oaths.

Does such oath-taking intrude on our civil liberties? I don’t think so. Here I’ll start: “I pledge not to murder my fellow Americans.” It’s a beginning – in what will be, alas, a long twilight struggle.