Safety in Numbers

Common humanity has ordained Europe's solidarity with the United States after the attacks on New York and Washington. But so has the chilling recognition of a common threat. As the investigations into the movements of the hijackers and other putative members of Osama bin Laden's al-Qaeda organization continued, evidence thickened that terrorist cells like the ones uncovered in Delray Beach, Florida dot Europe as well. Germany alone may be home to as many as 100 "sleeper" agents.

Europe has no symbol of military might like the Pentagon, no emblem of international commerce like the World Trade Center, no...