North Korea has explicitly defined the terms of its denuclearization agreement, leaving the United States with an ultimatum likely to define an unprecedented peace process as it enters a new year experts said would likely be filled with highs and lows for diplomacy in Northeast Asia. As a historic warming between Cold War–era rivals North and South Korea approached its one-year mark, the U.S. has found greater difficulty than its Pacific ally in establishing common ground with the notoriously reclusive government in Pyongyang. Still, President Donald Trump and North Korean supreme leader Kim Jong Un have made unprecedented headway in an attempt to solve the decades-long dispute between their nations. A commentary published Thursday in the official Korean Central News Agency outlined exactly what the young ruler meant when he agreed to abandon his nuclear weapons at a landmark conference alongside the Republican leader in June. Angered by continued U.S. sanctions and a refusal to declare peace ahead of what the State Department has defined as a “complete, verifiable, irreversible denuclearization,” KCNA contended that Washington’s recent actions could only be chalked up to the “misguided understanding” that only North Korea, officially known as the Democratic People’s Republic of Korea, and…