American presidents have long asked allies to pay more for their own defense—often with lackluster results. But both the U.S. and South Korea now face strategic challenges so large and complex that neither country can afford to allow the status quo to continue. That’s the context of America’s discussions with South Korea about a new special measures agreement.

The U.S.-South Korea alliance is the linchpin of peace and prosperity in Northeast Asia. Shared values of democracy, the rule of law and open economies form the foundation of an alliance that is as vital today as it was in 1953. America’s longstanding commitment and presence have enabled South Korea to develop a vibrant democracy and the world’s 12th-largest economy. Together, we celebrate this success.

In past decades South Korea has made major contributions to the alliance. It has modernized its fighter aircraft and enhanced antisubmarine and ballistic-missile defense capabilities. President Moon Jae-in’s government increased South Korea’s defense budget by 8.2% in 2019 and intends to raise it by a further 7.1% annually until 2024. South Korean forces have deployed in support of U.S.-led coalitions in places such as Afghanistan, Iraq and the Persian Gulf. South Korea also intends to procure military equipment that reflects a commitment to force modernization. The U.S. is grateful for these contributions.

But as sovereign allies, we must find a better way to share the costs of defense with South Korea and secure a stable and prosperous future for the Korean people. We are in an age of unprecedented threats that demand robust responses and team efforts. As a global economic powerhouse and an equal partner in the preservation of peace on the Korean Peninsula, South Korea can and should contribute more to its defense.

Today South Korea bears no more than one-third of the costs most directly associated with the stationing of U.S. forces on the Korean Peninsula. As these costs rise, South Korea’s share is shrinking. Moreover, these narrowly defined costs are only one part of the picture. America’s contributions to South Korea’s defense in this highly technological age—including some advanced capabilities Seoul still needs to acquire—far exceed the cost of U.S. “boots on the ground” and constitute a far larger burden for the American taxpayer than meets the eye.

The current special measures agreement captures only a portion of the cost of defending South Korea. The U.S. believes it should cover more. As we improve the burden-sharing arrangement, both sides will benefit. More than 90% of South Korea’s cost-sharing contributions currently go right back into the local economy in the form of salaries for South Korean nationals employed by U.S. Forces Korea, construction contracts, and other services purchased locally to sustain an American presence. It’s good for both nations.

Right now the two countries are again engaged in tough negotiations. The U.S. remains firmly committed to reaching a mutually beneficial and equitable agreement that will strengthen the alliance and combined defense far into the future. South Korea’s taking on a greater share of the load will ensure the alliance remains the linchpin of peace and prosperity on the Korean Peninsula, in Northeast Asia—and across the world.