The Donald Trump White House will have a fairly crowded foreign policy roster to deal with. From what has been said of the president-elect’s agenda for his initial months in office, Russia, the threat of ISIL and the ongoing turmoil in the Middle East, tensions in the South China sea, and his promises to renegotiate or abandon certain international trade pacts are likely to be his top priorities. South Asia does not seem to have made this list. And yet, the region presents some of the gravest threats to global security. Islamist terrorists and the conflict in Afghanistan remain huge challenges. But even greater is the danger posed by the threat of nuclear war between India and Pakistan.

The world has recently been reminded of just how tenuous the India-Pakistan relationship remains. Bilateral tensions have been alarmingly high since a September 18 terrorist attack in Uri in the disputed territory of Kashmir killed 19 Indian soldiers. India blamed Pakistan, and responded by using military force inside Pakistan-controlled territory. Since that incident, both sides have continued to exchange fire across the Line of Control that divides Indian and Pakistani Kashmir, resulting in significant military and civilian casualties. The situation flared up significantly last week after India claimed that Pakistani commandos had killed three Indian soldiers. Days earlier, Pakistan reported that it had lost seven soldiers to Indian firing in one night.

India and Pakistan are the only regional nuclear states in the world to be locked in an acutely crisis-prone relationship. Heightened crises offer terrorists the most realistic opportunities to breach Pakistani and Indian nuclear security protocols and gain access to their arsenals. Further, experts predict that an India-Pakistan nuclear exchange could “blot out the sun, starving much of the human race.”. It could be the end of the world as we know it.

The dangers of an India-Pakistan crisis going nuclear have been repeatedly highlighted in simulations and scenario exercises sponsored by the U.S. government in recent years. These exercises concluded that a crisis can escalate to an active conflict with relative ease and that once underway, India and Pakistan do not know how to keep a war limited. A number of the simulations have ended with Indian and Pakistani nuclear strikes against each other.

In the past, India and Pakistan have derived some of their confidence about limiting wars from their expectation of a U.S. role that would force their opponent to back down. They have tested this proposition at least three times since their May 1998 nuclear tests ushered in South Asia’s overt nuclear phase. A year after those tests, India and Pakistan were involved in the first limited war to have occurred between nuclear states since the 1969 Sino-Soviet Ussuri river clashes. Pakistan clandestine incursion into the Kargil region in Indian Kashmir led to a contained conflict. Unable to dislodge Pakistani troops in the initial weeks of the conflict, the Indian military reportedly came within minutes of launching air strikes inside Pakistani territory and the army had orders to prepare to cross the Line of Control at short notice. Either move could have led to swift escalation of the war. U.S. diplomacy proved critical in ensuring an end to the crisis. Alarmed by an Indian ultimatum to U.S. President Bill Clinton, Clinton threatened Pakistan with isolation and ultimately succeeded in getting the Pakistani prime minister to agree to pull out his troops in return for a promise that he would encourage resumption of India-Pakistan dialogue, including on Kashmir.

A terrorist attack on the Indian parliament in December 2001 triggered the next crisis. It brought a million Indian and Pakistani soldiers eyeball-to-eyeball on the international border for ten months. India was reportedly on the verge of punishing Pakistan militarily three weeks into the crisis. Influential voices in India urged action under the pretext that the United States would intervene to prevent Pakistan from escalating, and even physically prevent Pakistan from using nuclear weapons if came to that. American diplomatic engagement was crucial in disabusing Indian leaders of this notion. Washington consistently urged Indian restraint and put pressure on India by, for instance, issuing travel advisories that hurt it economically, while forcing Pakistan to acknowledge the presence of anti-India terrorists on its soil and acting against some of them. Lacking realistic military options and able to point to Pakistan’s unprecedented acknowledgment on terrorism as a success, India eventually de-mobilized.

A promising bilateral peace process between India and Pakistan followed, but it eventually broke down in the wake of multiple terrorist attacks in the Indian metropolis of Mumbai in November 2008. The attacks, perpetrated by the Pakistan-based Lashkar-e-Taiba, brought the two countries “fleetingly close” to major war yet again even as India showed remarkable restraint and avoided any major military mobilization. The United States was again at the forefront, urging Indian restraint and managing to get just enough anti-terrorist action from Pakistan against those accused in the Mumbai attacks to let the tensest moments of the crisis pass.

The Uri episode has transformed the South Asian crisis environment in at least one major way. By conducting targeted strikes inside Pakistani Kashmir in the wake of the attack, India has signaled a break from its long-held policy of strategic restraint. Previous Indian leaders threatened such retribution, but none ever executed it. By sending Indian troops into Pakistani territory to strike alleged terrorist targets, Prime Minister Modi has broken the taboo. His approach seeks to compel Pakistan to put a permanent end to cross border terrorism by actively raising its costs for allowing terrorists to operate from its soil. In the short run however, the combination of continuing terrorism and India’s assertiveness makes the prospects of full-blown India-Pakistan crises, and escalation, more likely.

Specifically, the next significant cross-border terrorist attack in India could put New Delhi in a bind. Given that the Modi government struck a triumphant chord and declared victory in the wake of the post-Uri military action, another terrorist incident would confirm a failure of this approach to deter terrorism. Prime Minister Modi would likely face immense public pressure to do more to punish Pakistan. Pakistan absorbed the post-Uri Indian strike without overtly striking back, but in doing so, its leadership expended immense political capital. Pakistan would therefore find it extremely difficult to hold back next time round, especially if the quantum of Indian use of force is greater. A tit-for-tat escalatory dynamic could easily be unleashed in such a crisis scenario.

There are other factors that promise to make these crises more dangerous than the previous ones. India and Pakistan continue to grow their nuclear arsenals at a fast pace. India has also actively worked to create limited war options against Pakistan under the nuclear overhang. New Delhi believes there is room to use force against Pakistan without breaching nuclear red lines. But Pakistan now possesses tactical nuclear weapons that could be used as battlefield weapons against Indian conventional forces. Pakistan’s nuclear threshold has always been ambiguous, and the danger of India inadvertently crossing it cannot be ruled out. Tactical nuclear weapons will likely lower Pakistan’s nuclear threshold further.

These dynamics will reduce the time and space available to U.S. interlocutors of influence outcomes, making America’s ability to prevent an ongoing, fast-paced South Asian crisis from escalating far from certain. Further, U.S. leverage during a future crisis depends entirely on the faith India and Pakistan are willing to put in its crisis brokering. The previous crises saw the South Asian nuclear rivals ultimately defer to U.S. diplomacy in return for promises of U.S. support. However, these U.S. attempts, successful as they were, dented America’s credibility with both sides. The United States promised India that it would press Pakistan to ensure the absence of cross-border terrorism but failed to do so. Pakistan’s actions against terrorists during the 2001 2002 and 2008 crises proved to be temporary and were reversed after tensions subsided. India’s strategic elite have therefore openly questioned the merits of banking on U.S. diplomacy in crisis situations since the Mumbai episode. Pakistan felt disappointed as it never received meaningful U.S. support to get India to negotiate on their outstanding bilateral disputes. Pakistan’s fast-deteriorating relationship with the United States also makes it less likely to perceive Washington as a neutral broker in future crisis iterations. Many in Pakistan believe that the United States can no longer be relied upon.

The context poses a serious dilemma for U.S. policy makers. As the global leader, the United States cannot afford to ignore a South Asian crisis that risks going nuclear. The region is home to one-fifth of humanity, including hundreds of thousands of U.S. citizens and their immediate families. Close to 10,000 troops and many more private contractors are still stationed in Afghanistan, and any number of U.S. forward bases in the region’s vicinity will also be directly threatened by the fallout of any nuclear incident in South Asia.

Washington’s policymakers must think outside the box. The current U.S. policy of engaging the India-Pakistan equation from crisis to crisis and merely firefighting at times of heightened tensions is unsustainable. Crises will continue to recur unless their deeper causes are addressed, and the growth of Indian and Pakistani nuclear arsenals will make them progressively more difficult to manage. A sustainable policy approach therefore requires the United States to go beyond mere crisis management and proactively facilitate crisis prevention by tackling these deeper causes. Two factors stand out as the principal enablers of conflict: terrorism and outstanding disputes between the two countries. A policy approach that combines the two has not been tried before but offers the best chance of success. The United States should take a firmer stand on any form of terrorism that can thrust India and Pakistan into crises. It must also make clear to Pakistan the reality that it will not be able to hold India back from using force in the wake of future cross-border attacks. Simultaneously, the United States must offer greater support to efforts aimed at resolving India-Pakistan disputes, like Kashmir, that underpin much of the motivation for cross-border terrorism. As a first step, the United States could encourage re-initiation of the India-Pakistan backchannel negotiations on Kashmir that brought the two sides close to an agreement before their bilateral peace process stalled in the wake of the Mumbai attacks.

The many competing foreign policy demands for the next U.S. administration notwithstanding, the Trump White House must make a normalized India-Pakistan relationship a top foreign policy priority. No other issue risks causing as much damage to the world, and to America’s credibility as its effective leader, as the prospect of an India-Pakistan nuclear exchange. On the other hand, normalization of their ties promises a more stable Pakistan less worried about Indian presence in Afghanistan and therefore more willing to support U.S. interests there. Normalization would also transform a jaundiced nuclear relationship that has held India back from becoming a truly global power.

Moeed Yusuf is Associate Vice President for the Asia Center at the U.S. Institute of Peace in Washington, D.C. He is the author of an upcoming book on South Asian nuclear crises, Brokering for Peace: Third Party Roles in Regional Nuclear Crises.

Image: SyedNaqvi90