Though North Korea has been a persistent U.S. foreign policy challenge for decades, during 2017 the situation evolved to become what many observers assess to be a potential direct security threat to the U.S. homeland. In July 2017, North Korea apparently successfully tested its first intercontinental ballistic missiles (ICBMs). Some observers assert that North Korea has, with these tests, demonstrated a capability of reaching the continental United States, although others contend that these tests have not yet in actuality proven that the DPRK has achieved intercontinental ranges with its missiles. Regardless, these developments, combined with the possibility that the regime in Pyongyang has miniaturized a nuclear weapon, suggest that North Korea could now be only one technical step—mastering reentry vehicle technology—away from being able to credibly threaten the continental United States with a nuclear weapon. Some estimates reportedly maintain that North Korea may be able to do so by sometime in 2018, suggesting that the window of opportunity for eliminating these capabilities without possible nuclear retaliation to the continental United States is closing. Combined with the long-standing use of aggressive rhetoric toward the United States by successive Kim regimes, these events appear to have fundamentally altered U.S. perceptions of the threat the Kim Jong-un regime poses, and have escalated the standoff on the Korean Peninsula to levels that have arguably not been seen since at least 1994. In the coming months, Congress may opt to play a greater role in shaping U.S. policy regarding North Korea, including consideration of the implications of possible U.S. actions to address it. The United States has long signaled its preference for resolving the situation with diplomacy, and has used economic pressure, in the form of unilateral and multinational economic sanctions, to create opportunities for those diplomatic efforts. Various Trump Administration statements suggest that a mixture of economic pressure and diplomacy remains the preferred policy tool. To a greater degree than their predecessors, however, Trump Administration officials have publicly emphasized that "all options are on the table," including the use of military force, to contend with the threat North Korea may pose to the United States and its allies. Consistent with the policies of prior Administrations, Trump Administration officials have also stated that the goal of their increased pressure campaign toward North Korea is denuclearization—the removal of nuclear weapons from the Korean Peninsula. If the Trump Administration chooses to pursue military options, key questions for Congress include whether, and how, to best employ the military to accomplish denuclearization, and whether using military force on its own or in combination with other tools might result in miscalculation on either side and lead to conflict escalation. Intended or inadvertent, reengaging in military hostilities in any form with North Korea is a proposition that involves military and political risk. Any move by the United States, South Korea, or North Korea could result in an unpredictable escalation of conflict and produce substantial casualty levels. A conflict itself, should it occur, would likely be significantly more complex and dangerous than any of the interventions the United States has undertaken since the end of the Cold War, including those in Iraq, Libya, and the Balkans. Some analysts contend, however, that the risk of allowing the Kim Jong-un regime to acquire a nuclear weapon capable of targeting the U.S. homeland is of even greater concern than the risks associated with the outbreak of war, especially given Pyongyang's long history of threats and aggressive action toward the United States and its allies and the regime's long-stated interest in unifying the Korean Peninsula on its terms. Some analysts assert that preemptive U.S. military action against North Korea should be taken when there is an "imminent launch" of a North Korean nuclear-armed ICBM aimed at the United States or its allies. Other analysts downplay the risk of North Korean nuclearization; few analysts believe that North Korea would launch an unprovoked attack on U.S. territory. Many students of the regional military balance contend that an overall advantage over North Korea rests with the United States and its ally, the Republic of Korea (or, ROK, commonly known as South Korea), and that U.S./ROK forces would likely prevail in any conflict within a matter of weeks. Those analyses, however, also generally assume that neither China nor Russia would become engaged in the conflict. Should China or Russia do so, the conflict would likely become significantly more complicated, costly, and lengthy. The toll of such a conflict could be immense, given that Seoul—with a population of approximately 23 million people, including American citizens—is within the range of North Korean artillery deployed near the demilitarized zone (DMZ) between the two Koreas. Should the DPRK use the nuclear, chemical, or biological weapons in its arsenal, according to some estimates casualty figures could number in the millions. Depending upon the nature of the conflict and the strategic objectives being advanced, U.S. military casualties could also be considerable. As a result, Congress may consider whether to support increased U.S. military activities—possibly including combat operations—to denuclearize the Korean peninsula, or whether instead to support efforts to contain and deter North Korean aggression primarily through other means. Any option would carry with it considerable risk to the United States, the region, and global order. As Congress considers these issues, key strategic-level questions include, but are not limited to, the following: Could the North Korean regime change its calculus, or collapse or otherwise transform, perhaps as a result of outside pressure, prior to its acquisition, or use, of credible nuclear-tipped ICBMs capable of holding targets in the continental United States at risk? What are the implications for U.S. relationships in the region if key allies are persuaded that the United States will no longer give the priority to regional security that it has thus far? What will be the cost implications, in terms of U.S. and allied financial resources, casualties, standing, and reputation, should hostilities break out, and how would those costs affect the ability of the United States to advance other critical national security objectives in other theaters? How do the risks associated with U.S. military action against North Korea compare with the risks of adopting other strategies, such as deterring and containing North Korea? Would a nuclear-armed Kim regime behave in a manner consistent with other nuclear powers? What would a nuclear-armed North Korea mean for longer-term national security decisions the United States faces? U.S. officials have been concerned about the threats North Korea poses to international order and regional alliances since Pyongyang's 1950 invasion of South Korea. The United Nations Security Council authorized a 16-nation Joint Command, of which the United States was a significant participant, to intervene on the Korean Peninsula to help repel North Korean forces. Shortly thereafter, when U.S. and allied forces pushed far into North Korean territory, China deployed its armed forces to assist the North. The parties eventually fought back to the 38 th parallel that originally divided the peninsula following World War II. Counts of the dead and wounded vary: according to the U.S. Department of Defense, more than 33,000 U.S. troops were killed and over 100,000 were wounded during the three-year-long Korean War; China lost upwards of 400,000 troops, with an additional 486,000 wounded; and North Korea's armed forces dead numbered around 215,000, with some 303,000 wounded. South Korea witnessed an estimated 138,000 armed forces and 374,000 civilians killed. Hostilities were formally suspended in 1953 with the signing of an armistice agreement rather than a peace treaty. Over the subsequent decades, the United States and its regional allies have largely contained the military threats to U.S. interests in Northeast Asia posed by North Korea. The United States and its ally South Korea have deterred three generations of the ruling Kim dynasty in Pyongyang from launching large-scale military operations. The U.S. security commitment to, and relationship with, the Republic of Korea has helped South Korea to emerge as one of the world's largest industrialized countries and, since the late 1980s, a flourishing democracy. South Korea today is one of the United States' most important economic and diplomatic partners in East Asia and globally. With respect to the Korean Peninsula itself, two key components of U.S. policy have been the U.S.-ROK Mutual Defense Treaty, along with the presence of some 28,500 U.S. troops in South Korea. Congress has supported the overall U.S. security approach to Northeast Asia, with the Senate approving defense treaties (and their revisions) with South Korea and Japan, and Congress providing funding for and oversight of the forward deployment of U.S. troops in both countries. U.S./ROK efforts, however, along with those of other countries, have to date failed to compel the DPRK to abandon its nuclear weapons and ICBM programs. Since Pyongyang began undertaking its weapons of mass destruction (WMD) acquisition programs in earnest in the 1980s, the United States and the international community writ large have employed a range of tools, including diplomacy, sanctions, strengthening of the capabilities of U.S. political and military alliances, and attempts to convince China to increase pressure on the DPRK to change its behavior. Around 90% of North Korea's trade is with China, which arguably gives Beijing significant leverage over Pyongyang. Some argue that these efforts have slowed but not stopped North Korea's drive toward developing a nuclear ICBM capability. The Trump Administration, as did the Obama Administration before it, places significant emphasis on expanding economic and diplomatic sanctions on North Korea and third-party entities that deal with North Korea. At the U.N. Security Council, the United States led efforts to pass eight sanctions resolutions, including the most recent, Resolution 2375, which was adopted in September 2017.