Formed by treaty in 1949 to defend Western Europe against the threat, real or perceived, of Soviet aggression, NATO has become the de facto defender of Ukraine's territorial integrity 30 years after the end of the Cold War. In this episode, historian Andrew Bacevich, the president of the Quincy Institute for Responsible Statecraft, discusses NATO's strategic drift and the folly of its eastward expansion. The alliance's mission evolved from the containment of the USSR to humanitarian interventions and fighting terrorism, first in the Balkans and then in Afghanistan and Libya. And now, as Russia threatens to invade Ukraine, fundamental questions surround NATO's ultimate purpose. Bacevich says the U.S. should leave the alliance, recognizing that Ukraine's territorial integrity is not a vital national security interest.