The struggle for the soul of Europe today is every bit as dire and consequential as it was in the 1930s. Then, in Weimar, Germany, the center did not hold, and the light of civilization nearly went out. Today, the continent has entered yet another “Weimar moment.” Will Europeans rise to the challenge posed by radical Islam, or will they cave in once again to the extremists?

As an American living in Europe since 1998, Bruce Bawer has seen this problem up close. Across the continent—in Amsterdam, Oslo, Copenhagen, Paris, Berlin, Madrid, and Stockholm—he encountered large, rapidly expanding Muslim enclaves in which women were oppressed and abused, homosexuals persecuted and killed, “infidels” threatened and vilified, Jews demonized and attacked, barbaric traditions (such as honor killing and forced marriage) widely practiced, and freedom of speech and religion firmly repudiated.

The European political and media establishment turned a blind eye to all this, selling out women, Jews, gays, and democratic principles generally—even criminalizing free speech—in order to pacify the radical Islamists and preserve the illusion of multicultural harmony. The few heroic figures who dared to criticize Muslim extremists and speak up for true liberal values were systematically slandered as fascist bigots. Witnessing the disgraceful reaction of Europe’s elites to 9/11, to the terrorist attacks on Madrid, Beslan, and London, and to the wars in Afghanistan and Iraq, Bawer concluded that Europe was heading inexorably down a path to cultural suicide.

Europe's Muslim communities are powder kegs, brimming with an alienation born of the immigrants’ deep antagonism toward an infidel society that rejects them and compounded by misguided immigration policies that enforce their segregation and empower the extremists in their midst. The mounting crisis produced by these deeply perverse and irresponsible policies...