Definition: In this task, you will be presented with a passage and have to answer a question based on your understanding of the events inferred from the passage. Try to find the best answer that is most likely to fill in "_". Note that the URLs in the text have been replaced with [Link].
Input: It's the war that never really ended -- leaving the Korean peninsula splintered in 1953. The brutal war that raged 60 years ago killed more than two million Koreans, separated thousands of families, and created the world's most heavily fortified border. It also drew the alliances that exist today. The armistice agreement that ended the war is a truce, rather than a peace treaty. Starting on Tuesday, North Korea threatened to dismantle the armistice, as it has done so in the past. In 2009, North Korea said its military would no longer be bound by the agreement because South Korea was joining a U.S.-led anti-proliferation plan. In 2003, Pyonyang's official Korean Central News Agency (KCNA) announced that it may have "no option" but to stop honoring the armistice because of the United State's "persistent war moves."A brutal civil war 60 years ago drew the alliances that exist todayNorth Korea has threatened to end armistice in the pastWar killed more than 2 million Koreans, separated thousands of families 
 Question:This time, KCNA declared that come March 11, North Korean forces will "completely declare invalid" the armistice agreement, because "the _ imperialists and the south Korean puppet forces" have violated it.

U.S.