President Trump stands with South Korean President Moon Jae-in at a signing ceremony for the United States-Korea Free Trade Agreement during the U.N. General Assembly on Sept. 24, 2018, in New York. (Evan Vucci/AP)

President Trump has adopted a desultory and dismissive attitude toward South Korea, part of his larger tendency to question the utility of long-standing U.S. alliances. Trump’s behavior, coupled with the potential for a historic formal declaration ending the Korean War, puts into stark focus the status of the 25,000 U.S. troops stationed on the Korean Peninsula.

The potential for replacing the Korean Armistice Agreement with a formal peace treaty is unclear. But if it happens, such a deal might prompt Trump to draw down, if not simply remove, these U.S. forces. After all, he has long been on record recommending such action.

Some would argue that the move would be justified, because reduced tensions and a peace treaty would eliminate the threat from North Korea that U.S. troops have been in place to deter.

But such thinking misses an important distinction: The institutional structure surrounding the armistice agreement is different from that which underpins the U.S. military presence. Although there is overlap between the two, the former could be dissolved without necessarily undoing the latter. And many contend that American interests far beyond South Korea strongly argue for keeping U.S. troops in place.

From the Korean War until the 1970s, the U.S.-led United Nations Command (UNC) was solely responsible for supervision of the armistice agreement and defense of South Korea. Under this arrangement, the U.S. four-star commander in chief of the UNC essentially held unilateral operational control over South Korean forces, based on a 1954 Mutual Defense Treaty.

However, events in the early 1970s cast doubt on the legal status and military utility of such an arrangement.

In October 1971, the People’s Republic of China replaced Taiwan as a permanent member of the U.N. Security Council. From this perch, Beijing began calling for the United Nations to leave Korea as well as abrogate a February 1951 U.N. General Assembly resolution, which had branded Communist China an aggressor against U.N. forces during the Korean War. Furthermore, in 1972, the 23rd Royal Thai Company departed from South Korea, leaving U.S. forces as the only remaining representative of the 16-member UNC.

At the same time, the UNC came under fire from scores of newly independent nation-states as a symbol of American neocolonial intervention in a sovereign third-world country. By mid-decade, these countries had transformed the formerly quiescent, pro-American U.N. General Assembly into a battleground for assertive Third World nationalism, often adopting decidedly nonaligned, if not outright anti-American, positions.

On Nov. 18, 1975, this agitation led the U.N. General Assembly to adopt two conflicting, though nonbinding, resolutions. Unsurprisingly, the pro-North Korea resolution called for the immediate end to the UNC and removal of U.S. forces. Yet, even the pro-Western resolution called for the replacement, by January 1976, of the 1953 Armistice Agreement with a proper substitute.

In this context, the Nixon administration moved to adjust the institutional and command arrangements in Korea. A National Security Council study examined a new policy that called for, among other things, the replacement of the commander in chief of the UNC with a new bilateral U.S.-Republic of Korea joint military command structure. The idea was to remove the United Nations from armistice-keeping as well as military defense on the Korean Peninsula.

This initiative aimed to place Washington “in a defensible position for possible debate of the Korean issue in the U.N. General Assembly this coming fall.” The United States could plausibly claim it was pursuing a more stable diplomatic settlement, and thus blame Pyongyang’s intransigence for its failure.

The Watergate scandal and Nixon’s resignation put Korea on the back burner. The issue slipped to the Carter administration after the fall of Vietnam, and the 1976 presidential campaign kept it low on the list of priorities.

Jimmy Carter entered office intent on withdrawing all U.S. ground combat forces from South Korea. A key element of Carter’s policy was the creation of a new combined command structure. The bilateral U.S.-Republic of Korea command would provide a cooperative means for dealing with the troop withdrawal, transfer of the defense burden to Seoul and serve as an acknowledgment of Seoul’s enhanced capabilities.

In November 1978, the United States and South Korea established the Combined Forces Command (CFC). This new structure replaced essentially unilateral American command over South Korean forces with joint guidance, though the United States maintained ultimate control. Although the United Nations Command continued to supervise the armistice agreement, the defense of South Korea was transferred to the CFC and the U.S.-ROK alliance.

Contrary to the recommendations made under Nixon and President Gerald Ford and even of his own advisers, Carter’s plan did not involve any serious diplomatic effort to replace the armistice with an alternative arrangement. Carter was simply determined to move forward with his campaign promise as originally envisioned. Indeed, this was one of the reasons Carter’s plan prompted such vigorous opposition from the foreign policy bureaucracy, Congress and American allies. It attempted to remove troops before finding a more permanent diplomatic settlement that eliminated the risk necessitating a troop presence.

Carter never got to remove American troops, but the CFC did situate their presence in a new, more robust bilateral institution. Over time, Seoul has gained more control over this apparatus, though the fundamental structure for defending South Korea remains intact. Indeed, one could argue that it is the most sophisticated and interoperable U.S. military alliance in the entire world.

But the UNC never disappeared, and the multilateral structure surrounding the Armistice Agreement still exists. The signatories to the July 27, 1953, agreement include the U.S.-led UNC, China and North Korea. South Korea had refused to sign. And it is this separate UNC that continues to help supervise the armistice agreement.

Although this sounds like technical detail — after all, the same U.S. four-star general heads up both commands — it is critically important for the current situation. Even if the armistice were replaced by a formal peace treaty and the United Nations Command dissolved, it would not have any impact on the combined American-South Korean command.

And for the U.S. foreign policy establishment, the need for that command would exist even with a peace treaty in place, because the rationale for the U.S. peninsular presence extends far beyond deterrence of Pyongyang. For successive generations of U.S. officials, this presence has constituted a highly symbolic node within a wider strategic, political and economic architecture. Indeed, Carter provoked such opposition when he attempted to withdraw the troops because of deep concern about how the move would harm broader American interests.

Such concerns are even more prevalent today, given the tension between the United States and China. But withdrawing these troops would also, it is feared, do grievous harm to U.S. credibility with its allies. Moreover, the innate complexity of the structures involved makes rapid change exceedingly difficult. Trump may be oblivious to this, but others are not. And if Bob Woodward’s recent account is any indication, these officials will continually delay Trump’s more impetuous attempts to undo institutions he simply does not understand.