In the 21st century, the greatest threat to the existence of the United States and its allies in Europe does not come from Russia, China, or North Korea. It comes from Islam. Islam is not merely a religion. It is a complete civilization with its own ethics, metaphysics, theology, and political theory in opposition to every other civilization on Earth. The Taliban, al-Qaeda, Boko Haram, the Muslim Brotherhood, and ISIS are merely brand names with a...