In Kenya, al Shabaab terrorists from neighboring Somalia stir up trouble and make grotesque threats. And we all know what bestial acts Sudan's Islamist government has perpetrated against black Christians over the decades.

Throughout the region, patience is wearing thin. Africa's impassioned forms of charismatic and Pentecostal Christianity won't turn the other cheek forever. The coming backlash could be ferocious (even dictatorships could exploit a vengeful popular mood).

The Islamist imperialists pushing to expand in Africa would do well to recall that Christianity has historical claims on such states as Egypt, Libya, Tunisia, Yemen and Saudi Arabia. Are they ready for mass violence aimed at a rollback? Or state conflicts?

A few years back, during one of four major research trips to sub-Saharan Africa, I visited the traditionally Muslim city of Mombassa on the old Swahili (Arab-slaver's) coast in Kenya. What I found was one of the sharpest religious juxtapositions I've seen in global travels.

Thanks to Saudi funding folly, there were far too many mosques for the congregants, so few hit critical mass. Islam in Mombassa felt sleepy, dusty and dull.

Kenya's Muslims were backward and listless. Condemned to poverty by poor educations (the Saudis pay Muslims to send their children to madrassahs, instead of to state schools), their culture seemed out of steam.

But Christianity blazed. Mega-churches couldn't contain all those who'd accepted Jesus as their Savior: City parks were packed with ecstatic worshippers every Sunday.

All along east Africa's Swahili Coast -- once a necklace of gems on the body of Islam -- the faith of Mohammed seemed like a museum exhibit in a neglected side room. The Christians -- from tribes Muslims had enslaved -- were the rising power.

As far as converts go, Muslims are being baptized (at great personal risk), but Christians aren't converting to Islam. Wahhabi Islam's rejection of joy just doesn't speak to Africans -- who even in misfortune seem incomparably alive.

Throughout sub-Saharan Africa, the old mysticism of folk religion glides easily into charismatic Christianity, but collides head-on with the intolerance of Wahhabism.

When I reached West Africa in later travels, it struck me that Islam never managed to penetrate the forests -- and not for lack of trying.

Forests, as we know from fairy tales, are the abode of magic -- for which Sunni Islam has no space. Africans can interpret Jesus as the greatest of conjurers, a worker of miracles, a miracle himself. Wahhabism, with its barracks regulations, can't compete.

I've never witnessed such religious fervor as I did in sub-Saharan Africa, from Zimbabwe north through Kenya and west to the Gold Coast. When Islamist terrorists attack African Christians, they're playing with a fire that burns white hot.

Pushed far enough, Christians will respond -- and it won't be pretty. The African church could become the church-ultra-militant.

Of course, a Christian crusade in response to jihad would be just fine with many Saudis and Gulf Arabs. They don't care about the suffering of individual Muslims -- only about Islam.

Thus the Saudis fund the provocative construction of mosques where there are few or no Muslims, from western Tanzania to eastern Tennessee. Every mosque helps stake a claim for the dar ul-Islam, extending the boundaries of the caliphate about which Islamists fantasize.

Meanwhile, the shared goal of the Saudis, al Qaeda, the Taliban and Somalia's al Shabaab is to prevent Muslims from integrating into non-Muslim host societies. In Kenya, a successful Muslim population that interacted and intermarried would be the worst outcome to Islam's commissars. Massacre would be preferable. And a violent Christian reaction would serve as propaganda to recruit the Islamist foot-soldiers who strap on the suicide bombs.

As radical Islam's hallucinatory ambitions continue to expand, the potential for tragedy on a grand scale soars. Religious strife could tear Nigeria apart, but elsewhere in Africa Muslims would swiftly find themselves on the losing end.

In Islamist extremism, we're confronted with a death-cult, not a faith -- while the vibrant Christianity of Africa pulses with life.

The collision appears inevitable.