Over the course of the twentieth century, American leaders have acted consistently to protect what they believed to be vital national interests, taking politically risky steps such as using or threatening to use massive military power, launch preventive wars or escalate conflicts to nuclear war. Up until the end of the Cold War, a shared appraisal of vital interests was the basis for the strategic partnership between the US and Europe. Now, the threat vector for the US has shifted to terrorism, the Middle East and northeast Asia. For Europe, it has simply disappeared. Without this common ground, another transatlantic crisis comparable to the dispute over Iraq seems entirely possible. If US leaders feel vital interests are endangered, they are unlikely to rely on NATO and the UN Security Council to help deal with the threat.