BELGIUM | FRANCE | GERMANY | ITALY | NETHERLANDS | NORWAY | SPAIN | U.K.

Home to an estimated 18 million Muslims, Western Europe has become the new and deadly battleground in the war on terror. Disenfranchised Muslims -- inspired by local radical imams and jihadist Web sites -- are taking up the cause of jihad, and Al Qaeda, once just a loose organization on the continent, has morphed into a powerful ideological movement.

Here is a country-by-country overview of the Muslims in Western Europe -- the societal factors that contribute to the sense of disenfranchisement, and the major terrorist plots and arrests. Plus interviews with top counterterrorism officials and Muslim figures in France, Germany, Spain and the United Kingdom, and special reports on the aftermath of the Theo van Gogh murder in the Netherlands and Norway's dilemma over what to do with Mullah Krekar, the founder of the terrorist organization Ansar al-Islam.