North Korea has presented one of the most vexing and persistent problems in U.S. foreign policy in the post-Cold War period. The United States has never had formal diplomatic relations with the Democratic People's Republic of Korea (the official name for North Korea), although contact at a lower level has ebbed and flowed over the years. Negotiations over North Korea's nuclear weapons program have occupied the past three U.S. administrations, even as some analysts anticipated a collapse of the isolated authoritarian regime. North Korea has been the recipient of over $1 billion in U.S. aid (though none since 2009) and the target of dozens of U.S. sanctions.