Nowhere is this dynamic more evident than in South Korea, which is acutely sensitive to the consequences of great-power contests, given that these have over the past century played a role in Japan’s occupation of Korea, the Korean War, and the division of the peninsula during the Cold War.

South Korea relies on its military alliance with the United States to counter the existential threat from North Korea, but does more trade with China than it does with the U.S. and Japan combined. Moon Hee-sang, the speaker of South Korea’s legislature, put it starkly when we met in Seoul in April: Asking whether South Korea will “choose either China or the United States” is like “asking a child whether you like your dad or your mom,” he noted. “We cannot abandon economy for the sake of security, and we cannot abandon security for the sake of economy.”

This strategy has underwritten unprecedented prosperity in the country, leading to reluctance among South Koreans across the political spectrum “to get involved in any big fights among big boys on the block … unless our survival is at stake,” Chun Yung-woo, a former national-security adviser to the conservative South Korean President Lee Myung-bak, explained to me. “We are split between our loyalty to the alliance and our chances to sustain the lifestyle we have been enjoying.”

What happens, though, when Mom and Dad can’t stop feuding, decide to spend some time apart, and start contemplating divorce? The South Korean government has in recent years repeatedly had to grapple with the very trade-off Speaker Moon dismissed as inconceivable.

Read: The U.S. can’t make allies take sides over China

Chung, the China expert, has identified at least seven instances in which Beijing and Washington have sought to coerce Seoul into their corner—matters such as South Korea’s involvement in dueling China- and U.S.-led multinational free-trade agreements, China’s new development bank, and American freedom-of-navigation operations in the South China Sea.

The real wake-up call came in 2017, when the Trump administration pressed current South Korean President Moon Jae-in to permit the deployment of a U.S. missile-defense system known as THAAD, which China considers a threat and Moon himself had criticized during his election campaign. Beijing retaliated by punishing South Korean businesses operating in China and halting Chinese tourism to South Korea. South Koreans became aware of “how harsh [the Chinese] can be in dealing with their small neighbors and how hollow their commitment to a peaceful rise actually turned out to be,” said Chun, the former official. “The romantic view of China is gone now.”

Forced to weigh the economy against security, Moon effectively selected all of the above, ordering a (still ongoing) assessment of THAAD’s environmental impact that has left the deployment in limbo and its attendant geopolitical questions unresolved. The South Korean government partially patched things up with China by promising to not carry out additional THAAD deployments or enter into a military alliance with Japan and the United States.